Unless the recurved tips are worked, they are just along for looks and do nothing for performance. if your boy draws a bow designed for a 28” draw length to 24”, he is not working the recurves. If you select a recurve, I would try to find him one that is designed for his draw length (plus some growing room). Off the top of my head, I don't know what that would be.
OTOH, a short longbow is a good performer no matter what the draw length. If money were no object, I would get him a 54” Shrew. I assume 54” Shrews are described by draw weight at 28”, as are most bows, so you would have to factor in his actual draw weight and draw length to buy the correct bow, as you are already doing.