Just my opinion, but since you have a two-year-old, I wouldn't be thinking about getting any new dogs any time soon. Dogs and little kids generally don't go well together. If you must, a Cairn Terrier, or West Highland Terrier (Westie) are both small, and normally do very well with children. Toto from the Wizard of Oz was a cairn terrier, and a Westie is essentially a white Cairn Terrier. They are usually friendly easily trainable. They are still a terrier though, and do what terriers do when strangers approach - make lots of noise. Some consider them to be especially smart due to their trainability, but actually it's the dumb dogs that are easier to train. Smart ones are more apt to refuse commands than dumbs one. Get a girl dog. Girl dogs are generally less aggresive than males, and may even treat your child like it's own.
Edit: I've a Westie and Cairn mix, she and my cat get along very well. The cat is actually larger than the dog.
Edit 2: When she was a pup, she had to go out several times a day. Now, at 3 years, unless there's something outside that's got her attention, like the sounds of children nearby, or other animals, she only needs to go out twice, once in the morning, once in the evening.