Generally, the parents have to be informed and be given an opportunity to object if they disagree with medications, or medical treatment of their child(ren). However, the court will make the final determination after it hears from all the parties involved, as well as reviews any statements from doctors, testimony from temporary custodians, etc. The court's decision will be based on what's in the best interest of the child. If the custodians are not notifying you of when the child is going to the doctor or the E.R., you can ask the court to order the custodians to inform you of these events. Unless there is a restriction on your contact with the child, most likely the court would allow you to be present for doctor visits, etc.
Sign up to receive a 3-part series of useful information and advice about child custody law.