Section 8- two bedroom to three bedroom voucher?

First I live in the state of Georgia. Atlanta metro area. I have a 2 bedroom section 8 voucher but want a three bedroom. Because my son is 12 almost 13 and my little girl is 6. Shouldn't they be in separate rooms? So, shouldn't I be able to upgrade to a 3 bedroom voucher? I know some counties have changed their rules about boys and girls sharing a room, like Dekalb county(they changed it to where a boy and a girl have to share a room). But what about Fulton or Clayton counties have they changed to rule also?