The screen is made of hardened plastic but with excessive force, it can break. The watch comes with a pre-installed screen protector to avoid this as much as possible.
You can purchase a screen protector from us here which offers added protection, but if you feel your child has an above-average chance of using un-controlled excessive force, we would recommend taking your Angel Watch to a mall kiosk.  They can professionally install a heavy-duty screen protector that will make the watch even more tough.  If this is a risk, it might be worth doing as breakages are not covered by your warranty.