How to get flat, cored stomach for teen girls?

Crunches, sit ups... The usual. They'll flatten your stomach... If u don't have a flat one. But of coarse it will take some time for it to get perfectly flat(: And try to do them daily like in the morning (I think it's better well cuz I do them in the morning?). U might notice like a 2 maybe 4 pack but nothing like a 6 or 8! Unless u realllly work out often