Or am I just easily entertained? Could be. Anyway, go to this website, Make My People Sing, and either you or your kids will be entertained forever. And if it's your kids, invest in some earplugs.
As a side note, I've recently seen this done with 4 horses as well. It's funny too.
Be warned though, whoever plays this needs to have at least a tiny bit a rhythm. Otherwise it's just noise. Okay, it may just be noise anyway.