I'm sure you have seen your kids holding their mallets like this with their index finger on top.
I try to keep my kids from doing this by saying "Remember, no sneaky pointers!". I establish this in K from the very first time we play barred instruments. It's a quick easy reminder to correct mallet technique. For some reason my kids think it's really funny and they giggle every time!
And soon enough they are holding the mallets like this! Or, quietly reminding each other. It always gets me when I hear one of them using my words like a little teacher. :)