The law protects children outside the family much as it protects adults. The crucial right that society denies to children is that of autonomy - the right to decide for oneself. The exceptions to this are few. Normally, the adult is sovereign and, absent abuse or neglect, that adult is usually the parent.
Society makes the parent into legislature, court, and sheriff for the child.
Parents set the rules and may use reasonable coercion to enforce them. The case of religious behavior is no exception. As Justice Douglas complained in the Amish education cases, the religious freedoms recognized by the Supreme Court have been those of adults. No child has yet invoked the free exercise clause to challenge a parental decision to require or forbid specific religious activity. Nonetheless, this autocratic rule can properly be understood as a regime of children's rights, including religious liberty.