I think that there should be a counter for the children as to how soon they can start working (like with the nursing moms), only it should start counting down when child turns 13. For example, Wabu is 13 and you are wondering how much longer until he can start working, you could open his details screen and it would say "Time remaining until able to work: 23 minutes."
_________________________
If at first you don't succeed, you're in good company.

http://dragcave.net/user/lawman247