You don't. Only goes by age height gender and weight.
I think it might be of the assumption that your body is used to that amount of activity and your metabolism settles, so you don't need extra calories. There are exercise points for additional activity though.
The new system is designed that you are actually getting a bit more than you would on the old. As well as that you don't have to point fruit... so thats always an option if hes starvin!! lol