A question that's often asked is "Can I take an old set of adult clubs and fit it for kids by cutting down the shaft?" Our answer is "Yes, but it's not recommended." Here are three main differences between kids golf clubs and adult golf clubs.
Flex (how much the shaft bends when swinging) is important for getting distance on a golf ball. Cutting down an adult shaft to fit a child will change the flex of the shaft, so even senior flex shaft may turn extra stiff if cut enough. Children tend to have slower swing speeds so shaft that's too stiff for their swing speed will reduce the distance a child can hit the ball.
Most adult golf clubs are far too heavy for a child. All the forgiveness built into the 460cc driver and cavity-back irons won't help if your child can't properly swing the club. Kids golf clubs, if built right, are built to be lighter with a child's strength in mind.
Children have smaller hands so the adult-sized grips will make it difficult for the child to maintain a proper hold of the golf clubs. If the grip is too big, your child may have a harder time holding the clubs, causing unnecessary strain and difficulty. Kids golf clubs are designed with smaller grips and smaller shafts for those grips.
So while it's entirely possible for a child to use an adjusted adult set, it is not recommended as the child will experience much more frustration playing golf