I think it would be fun if new players start the game with a smaller avatar and it would grow a little bit with each level they gain, until at some level (15?) they're considered "grown up" and have a full size avatar. That way if you see a very little glitchen walking around you know they might be very new and need some help. Or if you see a little one doing something annoying like grabbing everything in a community garden without replanting or asking, you'd be a bit more patient with them because they're just kids and don't know any better.
Just to make clear, I'm not talking about real life kids appearing as kids, I'm talking about any new player appearing as a kid.