Herd immunity relies on everyone doing their part to protect the whole. Children who are immunocompromised should not be put in danger because some people don’t want to play by the rules of society and accept that science is science.
Every child that can be should be vaccinated. If not, they should not be in public schools.
Additionally, once a child reaches an age that they can make informed decisions for themselves, maybe 12-13, they should lawfully be able to go against their parents’ wishes and get vaccinated if they so desire.