Meet Mr. Wilson. He's a "hook" of sorts, made out of a re-purposed tennis ball.
Add a couple of grommets and a suction cup to a tennis ball with a slit in it and you have a pretty unique towel holder that kids can really appreciate. Or use it as an apron or smock hook in a kids space. Not sure you want to tackle a DIY project yourself? Loony Designs sells Mr. Wilson for 12 euros.