There are too many 'families' in this country where the child is in charge and the parents do whatever the kids want.
My daughter is nearly 5. A while back she refused to allow me to (appropriately)strap her into the (appropriate) seat. So I simply lifted her out the car, locked the car and went back indoors. She cried about not going out and was told simply, either get strapped in, or don't go in the car - you choose. Needless to say we now have no issue about wearing seatbelts.