I agree with Carolyn, that you're probably referring to jello, the generic name for Jello-O brand gelatine whose commercial goes: "Watch it wiggle; see it jiggle, Jell-O brand gelatine. Of all desserts, you'll love the one, that tastes just right and makes such fun. Make Jell-O brand gelatine and make some fun! J-E-L-L-O!"

That would be Jell-O (brand name), called jello generally, if you're talking about in the USA. There are certainly many commercials showing kids going crazy about the stuff!

In British English it is jelly. In American English, it is jello.

The thing they eat? I'm pretty sure you're talking about 'jelly'! You can search this word online and look at the pictures to make sure it's definitely what you mean :)

Yes, jelly is correct :)