Yes, as long as your child is a minor and you hold parental authority (patria potestad), parental responsibility or guardianship: the duty to care for them extends to their digital life. That permission has two limits, and they are legal ones too. Your child has a right to privacy, and that right grows with their age, so supervision has to be proportionate. And the UN Committee on the Rights of the Child asks that digital monitoring of a minor not be routine, indiscriminate or done without their knowledge. With an adult, including your child from the age of 18, doing it without their consent is a crime.
This is the general guide: it applies to the Spanish-speaking countries, all of them parties to the Convention on the Rights of the Child, and it also works for the United States, which has not ratified it but reaches the same place through its own laws and courts, as its guide explains. The article numbers and penalties of each country are covered in the guides for Mexico, Colombia, Argentina and the United States. Here you will find the common principle, what the UN said in 2021 about supervising a child's digital life, what changes with age, whether you have to tell them, why it is a different matter with an adult, and the rules in Spain, which has no guide of its own.
None of these laws mentions the phone, and they do not need to. All of them say that whoever holds parental authority must care for, educate and protect their minor child, and that duty reaches the apps. The Convention on the Rights of the Child calls it providing appropriate direction and guidance (article 5); Argentina's Civil and Commercial Code, the protection, development and comprehensive upbringing of the child while they are a minor (article 638). But the same Convention prohibits arbitrary or unlawful interference with the child's privacy and correspondence (article 16) and gives them the right to be heard according to their age and maturity (article 12), and national laws repeat it (Colombia's Code on Childhood and Adolescence, article 33). The key word is arbitrary: supervision with a protective reason and a reasonable scope is not arbitrary; supervision done out of habit, with no reason and no limit, starts to look like it. Legal, here, means a balance between two rights of the same child.
In 2021 the Committee on the Rights of the Child, which interprets the Convention, published its General Comment No. 25 on the digital environment. It says that parents' and caregivers' monitoring of a child's digital activity should be proportionate and in accordance with the child's evolving capacities (paragraph 76), and that any digital monitoring of a child should not be conducted routinely, indiscriminately or without the child's knowledge, always using the least intrusive means that serves the purpose (paragraph 75). And it asks parents for a balance between protecting the child and their emerging autonomy, based on mutual empathy and respect rather than prohibition or control (paragraph 86). It is not a law that a judge applies directly, but the official interpretation of the treaty. The honest answer fits in there: yes, but proportionate, not routine and with your child's knowledge.
The Convention says it in one sentence: parents guide the child in a manner consistent with their evolving capacities (article 5), and General Comment 25 adds that in the digital environment children act with more independence from their parents (paragraph 19). Argentina writes it with numbers: adolescent from age 13, and the more autonomy the child has, the less their parents represent them (Civil and Commercial Code, articles 25 and 639). Spain uses maturity: the Civil Code requires hearing children with sufficient maturity before deciding anything that affects them (article 154). As guidance, not as a legal threshold: at 8, direct supervision in plain sight; at 13 or 15, a reason, a scope and an agreement; at 16 or 17, only concrete risks. At the age of majority, 18 under the Convention unless local law sets it earlier (article 1), the legal basis disappears: the same act goes from care to crime, unless your adult child consents to it.
None of the rules cited here requires you to tell a minor child that their phone is supervised. But "not required" does not mean "it makes no difference"; there are three reasons to do it with their knowledge. The first is legal: your child has the right to be heard on what affects them, and nobody can have a say on a decision they know nothing about. The second is the UN: General Comment 25 asks that digital monitoring not be done without the child's knowledge (paragraph 75). The third is practical, and the guide on checking your child's phone without telling them develops it: supervision that a teenager discovers by accident destroys precisely the trust it was meant to protect. That is why this site recommends supervising with the minor's knowledge. The exception is acute risk, such as an unknown adult asking them for photos: you act first and talk as soon as the danger is under control. The guide on how to talk to your child about parental controls explains what to say at each age.
Everything above rests on parental authority, and that ends at the age of majority. With an adult (a partner, an ex, a child who has turned 18) there is no duty of care, and accessing their messages, intercepting their calls or installing an app on their phone without their consent is a crime in all five countries. Spain's Penal Code describes it this way: seizing another person's messages, intercepting their telecommunications or recording them without their consent in order to discover their secrets or violate their privacy is punished with one to four years in prison (article 197.1), and disclosing what was obtained, with two to five (article 197.3). Paying for the line or owning the device changes nothing; the country guides cite each one's article and penalty. The same article increases the penalties when the victim is a minor (197.5); the law protects your child's privacy against third parties too, and disclosing what you see on their phone is harm, not supervision.
Each country writes the same principle in its own articles, and each guide cites them with a link to the official source. Mexico: the General Law on the Rights of Children and Adolescents recognizes the minor's privacy and charges parents with guiding and supervising their habits (articles 76 and 103); the detail is in the Mexico guide. Colombia: the Code on Childhood and Adolescence defines parental responsibility and protects the minor's privacy and correspondence (articles 14 and 33); the detail, in the Colombia guide. Argentina: the Civil and Commercial Code regulates parental responsibility and progressive autonomy, with adolescence from age 13 (articles 25, 638, 639 and 646); the detail, in the Argentina guide. United States: the logic is the same, with a federal wiretap law and the laws of each state; its guide explains the parent's consent on the child's behalf and where recording calls requires everyone's consent. All four also cite the criminal article that applies with adults.
Spain has no guide of its own. The basis for supervising is parental authority under the Civil Code: it is always exercised in the children's interest, with respect for their rights, and it includes looking after them, educating them and providing them with a comprehensive upbringing (article 154). The limit is set by Organic Law 1/1996, which applies to anyone under 18 (article 1): it recognizes minors' right to privacy and to the secrecy of their communications, and orders parents to respect those rights and protect them against third parties (article 4). The same law calls for digital literacy that lets minors identify risks online (article 5): supervision is no substitute for education. With adults, the line is article 197 of the Penal Code, already covered. There is no age from which the child can veto the supervision: the test is maturity, the Civil Code requires hearing them before decisions that affect them (article 154) and Organic Law 1/1996 presumes it, for the right to be heard, from the age of twelve (article 9). In a real dispute, consult a family lawyer.
Three rules. Proportion: supervise what the risk justifies, with the least intrusive means; with a young child, looking together and the parental controls the system already includes, such as Family Link on Android, are usually enough. Transparency: your child should know what is looked at, why and until when, in writing and with a review date so the scope keeps shrinking; that piece of paper is your best backing if anyone questions it, and at 18 it ends or becomes a consented agreement. Real risks: unknown contacts, harassment, requests for photos, content that harms them; reading everything does not protect more and it destroys trust. Also: what you see stays with you, never in a parents' group chat, and a tool that keeps them from asking for help is too much, as the UN warns (paragraph 76). CatWatchful fits here only this way: on your minor child's Android, with their knowledge and a scope that matches their age, or on the device of an adult who has consented to it.
Until the age of majority, which the Convention on the Rights of the Child sets at 18 unless local law sets it earlier. But age does not work like a switch: supervision should be scaled back from around 13, and at 16 or 17 limited to concrete risks. The day they turn 18, it either stops or becomes an agreement with their written consent.
With a minor child in your care, yes, with the same limits as the rest of the phone: proportion to their age, a protective reason and never sharing what you read, because in every chat there is another person, often another minor. If they are under 13, look first at the guide on WhatsApp's managed accounts for minors; the guide on reading your child's WhatsApp legally explains the encryption and what can be seen.
None of the rules cited in this guide requires it. But the UN's General Comment 25 asks that digital monitoring of a minor not be done without their knowledge, and the Convention gives them the right to be heard on what affects them. In practice, too, supervision discovered by accident breaks the trust you were after; the guide on checking your child's phone without telling them develops this. Unless there is an acute risk, tell them before installing anything.
As long as you are a minor, yes: the law puts them in charge of caring for you, in the digital world too. But you have rights: to be heard on what affects you (article 12 of the Convention) and to supervision that is proportionate to your age, not routine and not done without your knowledge (General Comment 25). Ask them for an agreement with an end date; at 18 it ends. And if what they see is used to expose or humiliate you, that is not protection: talk to an adult you trust.
It depends on your legal situation. With guardianship or formal custody, the law treats you like the parents: Mexico's law imposes the same obligations on whoever holds guardianship or custody, in proportion to their responsibility (article 103), and the Convention names the extended family and guardians alongside the parents (article 5). If you only care for them in practice, the decision belongs to whoever holds parental authority: agree it with the parents, in writing.
The prudent answer is yes. Unless a court has ruled otherwise, both of you keep parental authority, and supervising your child's phone is a decision about their upbringing that is best made together; Mexico's law expressly asks parents who live in different homes to fulfil their obligations in a coordinated way (article 104), and the country guides cover the custody case. Never use their phone to monitor the other parent: if you access their communications it is a crime, and in any case it backfires in front of the judge.
This guide is general information about the legal framework shared by Spanish-speaking countries and the United States as of the review date, not legal advice. Each country has its own laws and, in many, each state or province adds rules; the country guides go into that detail. For a specific case (a custody proceeding, an emancipated minor, a criminal complaint), consult a family lawyer in your country.
Related guides: Is it legal to monitor my child's phone in Mexico? · Is it legal to monitor my child's phone in Colombia? · Is it legal to monitor my child's phone in Argentina? · Is it legal to monitor my child's phone in the US? · Is it illegal to check your child's phone without them knowing? · Can I read my child's WhatsApp messages legally? · Talking to your child about parental controls