I think it really depends. Honestly, most Yorkies I have ever met have "surprisingly" been good with kids. Definitely just always watch with caution! Have a "safe place" for dogs to go, such as an expen, a room, etc. Kids and yorkies can get along well, with supervision and the right kids/dog! It can be a good learning experience for both.
Jackson is great with most gentle kids (in fact he's more willing to go up and say hi to a kid than an adult), but he can be nervous around hyper active type kids. But what I usually do, to make it fun for both, is bring lots of treats. I usually have "strange" kids (to him) do tricks with him too, which they always find so funny, and he is most comfortable doing something he knows well.
I always love this video, of my little sister when she was 3 (excuse the messy room).