Is it legal for a pediatrician to withhold vaccinations without notifying the parent?
It is likely a violation of medical or professional ethics to withhold vaccines without notifying the child's parents: they did not provide the expected level of medical care; they did not get informed consent from you as to what they were doing. You could file a complaint with the state office that licenses doctors. But there is no legal action you could bring unless you can demonstrate an actual (not merely possible or theoretical) harm that you son suffered from this, since malpractice suits and other civil legal actions provide compensation for harm suffered: therefore, no harm, no case.