The best and most important tip I can give you when going to yard sales, auctions, or thrift stores with kids is...
BUY THEM A CHEAP $.50 TOY! every time!
Explanation: You might not want to spend money on a new toy or your kid might not even need anymore toys, but trust me, it is worth it. When my son has a new toy to play with when I am out pickin', it is a life saver. He plays with it the whole time. And it is funny, because every time we go out vintage pickin' he knows. He says, "I gonna go look at toys." LOL I play it up too! "Ok, Cayden. You can have one truck. Oooo look at this one, Cayden! This one is a RACE car!" ( he lovesssss anything automotive!) The $.50-$1 is nothing, when you think of having a wonderful, focused, and peaceful hunting experience.
Example pic! Content and happy.