International Covenant on Civil and Political Rights
Article 18
....
4. The States Parties to the present Covenant undertake to have respect for the liberty of parents and, when applicable, legal guardians to ensure the religious and moral education of their children in conformity with their own convictions.
https://www.ohchr.org/sites/default/files/Documents/ProfessionalInterest/ccpr.pdf
The US is a state party.
Be nice if that covenant was worded so an average person could understand it.