It depends on the Yorkie. Sammy loves everyone, even kids, and she's only 6lbs but she's tough. A 7-month old neighbor was all over her last summer, pulling her hair and trying to hug her and she could hardly contain her excitement. It think our only problem with Sammy will be teaching her not to lick faces
Loki is a nervous dog and he takes a while to adjust to everything. But he does fine with familiar situations and he is very trainable. We had 5 people (family members) over last night and he bounced around like a puppy trying to say hi to everyone and then ran to his corner to chew his stick and observe all the action
I can see him laying under a baby's crib watching out for his new "sibling"
But here's the deal - Loki is 4 and has had 2 years of obedience and Sammy is 3 and was raised with kids until she was a year old. So my suggestion is either to wait until your dog is well trained and out of the puppy stage (at least 2 years) before having children, or wait until your child is a little older (at least so you are not up all night with baby AND puppy) before getting a puppy. Do NOT get a puppy and then have a baby right away or the other way around if you enjoy your sanity. Housetraining a Yorkie is a full time job. You don't want to do babies and puppies together
Oh, and get a bigger Yorkie for sure. Sammy is 6 lbs and she's TINY - just because Yorkies come in 3, 4, 5 pound sizes does NOT mean 6 lbs is a big Yorkie! Don't go smaller than that. Loki is 12 pounds and he's a great size too.