These days with good special effects and makeup, it should be possible for a younger actress/actor to change their appearance that way. Of course an adult shouldn't try to play a child, though, or vice versa. That would just be weird.

Wow. In that case, I can kind of see why they would change the ages of the characters so drastically. Since the children are behaving in a very mature way anyway, I guess it wouldn't seem really out of place to just up their ages. But from 10 to 40 is quite a huge difference!