Multiple Federal Appellate Courts have found that children have a right to familial association with their parents and that these rights are fundamental rights. The Supreme Court has placed the right to free association into the category of First Amendment rights as the right of free speech would be meaningless without the right to associate with others. First Amendment rights as we know require enhanced scrutiny.
When both parents in divorce are fit, there is absolutely no rational basis for depriving the child of equal association rights with both fit parents. Doing so creates a second class child based on nothing more than the marital status of the parents. This as we know violates the Equal Protection Clause of the Fourteenth Amendment.