I waited til my kids was in a booster seat before I got the Mustang. IMO it would be a PITA getting them in and out of the rear seat.
But depending on how the child seat or base fits in the rear it should be doable. Best to try it out at the dealership with the seats you have.
The Mustang was the first car I bought that I didn't have to test child seats in before I bought it....