The lines on the head of your putter effect your aim, no lines aims up right, a top line a little more left, a bottom line more left and three lines the most to the left
Make sure your kids have equipment that is the proper size, for the same reason you wouldn’t buy them oversized skates to play hockey
What really differentiates players is their short game, and juniors should take a tip from the pros and spend at least half their practice time on the short game