My boyfriend's granddaughters, ages 4 and 6 sometimes visit our home. They have always gone straight to my aquariums and started hitting the sides of the tanks. The first time this happened, four fish were dead within 24 hours. I have asked the girls' mother to please not let the children hit the sides of the tanks--they can look, but not touch. Now my boyfriend and his daughter are insulted--they seem to feel the kids do not need boundaries when they come over. Is there any correlation to hitting/slapping the sides of the tanks hard, and demise of fish?