"Children eating fruit" would be „Dzieci jedzące owoce”. Here you put emphasis on the children more and use what they are doing as their description.
In "children eat fruit" or "children are eating fruit" you are pointing out what the children are actually doing.
And on a less serious note, "Children-eating fruit" would be „Owoce dzieciojady”. I'm pretty sure you will figure out the meaning. :)