Bright colours and friendly, happy fish in a sup $10 mobile. What more could you ask for? Best of all, if Ikea’s Korall mobile doesn’t suit your needs you can also have a look at their Minnen Lamm (lambs) or Barnslig (horses or hippos or something) alternatives.
Whichever you choose, I expect the bright, contrasting colours and downward figures will be a hit with your child.