"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. :)
Your false impression comes from the fact that the second "o" is stressed,
"o-wo-ce", that is why it sounds stronger and a bit longer than the first one.
Since the stress falls, most of the time, on the second from the last syllable, you will probably notice that in singular word "owoc" you have the same impression about the first "o", because this one is stressed now: "o-woc".