Breeds Of Dogs

Hey guys! I'm on a hunt for small breeds of dogs, my friend wants a small breed of dog and I'm planning to gift him one. Although I've came across some small breed of dogs such as pugs, maltese, beagle, chihuahua, havanese and papillon. I found them interesting but I want to search for some more. Anyone out there please come up with some names of the breeds of small dogs. Also give me some tips about their maintenance and trainability. My friend has a 4 year old son and i want anyone to tell me which breed of small dogs will be best compatible with a child of that age? Thanks!