I am a breeder and yes it is hard to find families with well behaved kids.
My Yorkies are on the small side but so were the Chihuahua's I bred. I have placed so many of my Chi's in wonderful homes with small kids. My Mikey was just a baby when I was breeding and he was the "Best" baby and then toddler around my Chi's! I do meet with the families and see how their children react around the puppies. Also see if the parents are constantly correcting. That is kind of a "no " sign to me! If the kids are careful without the parents saying anything then its usually a go. The parents looking at one puppy while the others are looking at the others. You can clearly see the behavior of the child. At least that is my experience. (It's almost like leaving the kid alone to see how he reacts, is he good and careful etc.) You know? You have to read between the lines. Gut feelings and such. I don't mind placing my Yorkies in homes with small children as long as I meet them, talk to them and so on. I know they aren't big Yorkies but they are sturdy and very healthy and happy! I hope this helps.