The trickiest part is getting their limbs to bend in the right spots.
Since they're so much shorter, the smallest deviation will seem quite jarring.
If you're going to practice drawing kids, practice drawing them doing things, like running and skipping, to get as many bent legs into each drawing as possible.
Other than that, they have large heads, with small noses and ears (which never stop growing, so old people have large ones) and large round eyes (your eyeballs don't really change size are you grow, just the holes you see them through).
