To correct this problem, one way is to do more vision training with one or two pieces. I will describe how to do vision training in my future book: "700 points in a year - a practical training manual for chess beginners and chess parents".
The second way is to solve large amount of one-move checkmate problem. My daughter solved her problem with this approach. She actually worked through a one-move checkmate book with 100 checkmate problems. Nowadays there are software to help practice one-move checkmate. My web store has the following titles: "Chess for Beginners: Elementary Checkmates I" and II, which have 40000 and 77000 mate-in-one exercises. I can guarantee that if your child goes through 10% of these exercises, s/he will rarely hang a piece.
The third way is of course to play more chess.