The basic difference of a chick starter and a meat bird starter is the protein level. The meat bird is formulated to promote more rapid growth. I would feed the meat bird starter with no reservations at this stage. It will help with feather formation and slow down feather picking which is rather common for this age group. If you are letting them out for a bit and giving kitchen scraps as treats, it's probably a better choice as it will help keep their overall intake levels closer to the ideal.