Hi, so this is something we see a lot, almost daily. If it's a child golfing, we will always say use a junior set, like the Callaway XT Teen Set (https://allkidsgolfclubs.com/collections/callaway-junior-golf-clubs/products/callaway-xt-10-piece-teen-golf-set-white) because it is made specifically for kids who are still growing and do not have the strength and power behind their swings like adults do. In this case, your son would be too small for the Callaway XT Set, but it would fit your daughter. It is normal to choke up a little on clubs, but it may be too much in this case since your son is 56 inches tall. There is never one size fits all, and in this case it's about the technology behind the junior clubs that allow kids to have success (clubs are forgiving, proper shafts, junior flex, the list goes on). Junior clubs are made for juniors, and generally speaking, adult clubs are made for adults because of their mature development physically.