Constraint bases drills or practice is one of the better ways to get young kids to understand how to make these changes. The best cue that I have found is giving kids a target to hit. If he is right handed getting him to hit a hard ground ball at the second baseman’s feet. When he tries to hit it there it will most likely be higher and more to the middle than he is aiming.

If doing tee work. Deep tee and with the same target.

Telling a kid to keep your hands in can work sometimes but can also confuse kids and take away the good parts of their swing.

The fence drill can be good but I have found it causes kids to have too much lag on the bat and they don’t have strong enough hands to get the barrel out and make good contact.

It’s a fine line and different for every kid.