Air travel security has changed dramatically since December 25, 2009. Pat downs are a regular part of the security process now. That doesn't mean that you will definitely receive a pat down, but you should be prepared for things to be different than they were before (including pat downs for adults and children alike).
My seven year old is extremely anxious about airport security at the best of times. He likes things to be as he expects them to be, and he won't like the fact that things have changed. We're doing our best to prepare him, but it's hard, given that we don't know exactly what is going to happen.