With an almost-two-year-old who just
loves the fish, we have to deal with this problem constantly. Any time he gets near the tank we say "gentle". (He learned "gentle" with the dogs and cats, which at least have a fighting chance!) He usually settles for just putting his hand on the tank. I really don't have a problem with that, since he's not chasing the fish or anything. Of course, there's still the fingerprint issue, but I can deal with that. As long as he doesn't slap the tank, the fish don't even seem to notice.
Of course, when we go to a fish store (or if we were to visit a friend with a tank), we are "just looking". (He learned that with the Christmas tree -- we bought the most prickly spruce we could find!) But just like anything else, if parents don't take the time to teach their children to listen or to follow a few simple rules/commands (eek, makes it sound like dog training!), the child is not necessarily the one to blame.
Of course, there are plenty of adults who don't see any problem with tapping on glass, think the fish like it, or simply figure that fish are a lower-order animal, so why should we get so bent out of shape over it?
