What are some kid friendly little dogs?

Our old Schnauzer died and we are going to get a puppy this summer but we are not sure what kind to get. We want a little dog like knee size or below knees. Nothing above. We also have little kids at our house so we need a kid friendly dog. We also have a Cairn Terrier (Toto) so the new puppy needs to be dog friendly also. What are some playful friendly little breeds?