if you are asking what I think you are asking: meal plans are based on age of the diner, NOT what menu they order off of.
that means if Universal considers an 11 year old an adult for ticket pricing purposes, then they must also have a adult dining plan.( just like Disney).
if you wish to pay a la carte, then it doesn't matter what menu they order off of( of course buffets will reflect the correct pricing based on age again, just like Disney)