@DrewDad,
Well, they can call it 'mandatory' or even insist that it's a 'law' to be complied with prior to entering public school or child care facilities, but if they offer easily obtained exemptions, then is it really mandatory?
Vaccination can be strongly recommended, I'd think, but, constitutionally, a public school wouldn't have the right to deny admission based simply on a child's immunization record.
In the case of California, what they
do have a legal right to do is deny admission to an unimmunized child during an
outbreak, if the record shows that child has not been immunized against
that particular disease. But, that child has every right to return to school once the outbreak is diminished.