Hey Tweezers, my wife and I have a miniature Schnauzer. Here's a picture of her at 6 months old.
They are very smart dogs, and very lively. Totally into squirrel "hunting." More like chasing! At 3 years old, she's just under 15 lbs., about 12"-13" high at her shoulders, and maybe 18"-20" long. It's best to acclimate them to kids when they are very young puppies. Our dog was from a rescue agency, and the dogs tend to have emotional issues that take a long time to overcome. For a household with kids, I would recommend going to a reputable breeder and finding the most relaxed and happy puppy they have.
A similar sized dog that I'd also recommend is a Welsh Terrier.
Bigger dogs like Labs are great...very mellow and kid friendly.