[Addy]

With children under 11, one thing to keep in mind is proportions as we learned them are generally thrown out the window. Heads are bigger, eyes are even bigger than that, arms and legs are shorter/stubbier. And roundness. The basic proportions we learned for head size compared to the rest of the body is totally moot, too - the younger the child, the more extreme it gets, too.

As for older, that's hard to say. :'D Sharper edges, more lines on the face? Also showing their tiredness in posture can help for really old people.