They are probably doing this. Starting in their stance with the bat on the deltoid is a good short term fix if you can get the kids to buy into it.
at asa 12u nationals, we have several girls hitting the bottom of the ball. of course im looking for a quick fix lol. have used the "flat bat" drill in the past with the player facing the pitcher and swinging . started with bat on shoulder then with bat off shoulder. on or two are dropping their hands. any suggestions.