If your child gets a vaccine, they’re probably not going to feel so good. Infants are likely to be extra fussy and irritable. Children may run fevers and not want to go to school. Nurses will tell you to give them some Tylenol to help them lower their fevers so they feel better. Online, I’ve seen mothers PRE-medicating their children hours before their shots with Tylenol in hopes of heading off these problems beforehand.