J.L.
I have a shih tzu (10 years old now). He was very good as a puppy-3 years when he was around my nephews who were babies/toddlers. After that he has limited exposure to kids, as my nephews moved out of state. I now have an almost two year old of my own and he's pretty good with my son. If he gets pushed to the limit, he will threaten to bite, but he has never done. Most of the time he just runs from my son when he pushes the boundaries, but if he is trapped, he will show his teeth when he's being hit, hair pulled etc. We do a very good job of never leaving the dog and my son unattended with him, only because you just never know what my son will do to him. And I truly believe if my dog was exposed to kids all the time and didn't have a five year gap in the middle, he would be super tolerant of my son.
They are really good dogs and they dont' shed and are great for people with allergies since they have hair and not fur. Iwoudl get them one from a breeder though.