Could always get those trippy glofish haha.
Lol, I was actually thinking this too. My three year old has a ten gallon tank with those in it and absolutely loves them. I even tried to get him to pick something else last time I got him some fish but he refused to get anything but glofish. Lol. They "glow" pretty nicely if you get the blue LED light that goes with them. I've also heard that a black light makes them "glow" the best, but I haven't tried it yet.