Wow. He's going to be very small indeed. Are you planning to get another, bigger dog when your children grow up? Since Moshi is a therapy for the eldest, he might be able to learn more from a bigger, more powerful dog once the son is old enough.
Yeah they are a small breed, but surprisingly one of the oldest -- I believe as far back as 400 AD in the Chinese court; modern pugs are quite a bit different as they've been bred for specific traits (like cuteness!). I would love a big dog, I never really wanted a little one but we don't have the space for anything else at the moment, and the wife definitely does not want a big dog. Maybe when we have our own house, with a large area of land, then I'll get my big dog and it can have the run of the place. :) My neighbour has a Belgian Shepherd (~ 60cm, ~30kg) and they get on very well, but that thing is like a bear! Here I just snapped this for you, it's like a Where's Moshi? puzzle: