Dogs have been selectively bred for thousands of years, sometimes by inbreeding dogs from the same ancestral lines, sometimes by mixing dogs from very different lines. The process continues today, resulting in a widening in appearance without speciation, "from the Chihuahua to the Great Dane."
Some dogs will patiently put up with little children who pull their ears or accidentally poke them in the eyes, while others will not and map nip or bite back in defense. So if you want a dog who is excellent with children avoid breeds which may have a dominance streak or that have short tempers.
You do not have to have own a large house to own a large dog (although a tiny apartment is not going to be big enough for one of the giant breeds). If you can take him outside for a good hour of two of exercise every day... a large dog can live in a small house or apartment just fine.
Trust us, not all mixed breed dogs look like junkyard mutts (which come on, are pretty cute too). In fact, here is a rule of thumb: when one gorgeous dog breed mates with another gorgeous dog breed, the end results are -- wait for it -- pretty darn gorgeous. That is science, baby! Here are a number of wonderful examples of some of the most adorable mutts out there.