Since you have never had a dog before, DON'T get a puppy. Puppies are LOTS of work...you would be better off getting a more mature dog from a shelter...save a life. Seriously, these dogs are usually already housetrained, spayed/neutered, cratetrained, etc.....most are GREAT dogs.
Larger dogs usually do better with children...the small ones can get very nervous and sometimes snappy around children because of their quick, sometimes unpredictable movements.
NO dog, no matter what the breed or size, should be left alone, unattended with children...especially when you first get them....
You don't say whether your family is active (runners, swimmers, etc), but get a dog that fits your lifestyle....also fits where you live (if you live in an apartment, are you able to take it for walks?)If you get an active breed (one of the herding dogs or a lab, and don't give it enough exercise, they WILL be destructive....)
Most dogs shed...some a LOT (like German Shepherds, which is what I have), and require daily brushing and sometimes TWICE a day sweeping of the floors....the only "non-allergenic" dog is a poodle.....also, if you get one of the "cutesy" dogs, remember that grooming can get very expensive....
Choose wisely; do your homework......good luck.
Lifetime dog owner, rescue worker