My daughter is currently 7 and she rides in an 11 inch. We like the corriente buckaroo saddles. The stirrups actually go short enough and hold them in well. I recently just bought her a youth bob marshall. It's a 12 inch and still a bit big for her. Depends on the size of the kids too. 

My daughter is 7 and small for her size, she weighs 48lbs. We ordered her an 11" Bob Marshall youth cut with regular saddle parts (not the baby bob) She still has a lot of room to grow but it really holds her in with that deep seat.