I would follow it up. Your percentage is based on how many kids in care and wage and so on. It should be applied to all your children in care. So your two child percentage applies to both kids.
Perhaps they don't realise your children are siblings?

ETA: Then you probably only get the 2 child percentage on the days they both go to care on the same day? On the other day, it is the one child percentage? Hopefully BG will pop in and clarify.