Could you tell me what happens if I refuse to get a booster shot for my child upon entering school?

Depends . In some states you must vaccinate or face the childs exclusion from day care or state funded school systems. There is often a method of obtaining a waver based on personal or religious beliefs, but you should have it in hand at registration. Check with the special services section of the school system.
Booster immunization. Avoiding boosters is not a good idea as it helps in building up and maintaining the immunity your child has from the prior immunizations. If your child had no reactions to be scared about form prior immunizations, odnt avoid them now. If there were soem serious side effects, you should talk to your docotr about your concerns.There are truly very few contraindications.