I think that will depend entirely on the children, and the best suggestion I could offer if you're a
travel agent is to ask your client about their kids (and the parents).
My kids are now 14, 10, 10. They enjoy FutureWorld, but the World Showcase has always been a total snooze fest to them. It just wasn't for them. They liked the rides. Even the gift shops in WS are 90% ignored by them, there's very little that they have interest in. They'd much prefer to be in MouseGears or the World of Coke or the pin trader station. Their food tastes are not very adventurous, except for DD10, so the food tasting in the different countries isn't appealing to them either.. They're starting to have a little more interest in things in the WS, but it's still only very mild interest at best (in the past, we used to have to drag them back there, now at least they're willing participants). They never had interest in things like Kid Cot stations or Agent P, so we never did much of that either.
But as I said, ask the parents too. Some of our kids disinterest in WS also comes from our own feelings on it. Certainly, we have significantly more interest than our kids do. But even when DW and I have a date night alone in Epcot, we don't spend much time in WS. DW likes some of the street performers, and so do I. But as for going into each building and really walking around exploring, not so much. Again, not saying we totally ignore it, but it's only mildly interesting to us at best. Neither of us drink alcohol, we simply don't understand the attraction to it, so that is a total turn off to us (in fact we prefer to stay out of WS later at night). So as a whole, if you ask me to rate WS on a 1-10 scale, it would get maybe a 4 from us. Not tragically horrible, but really not something we go out of our way for. And that's purely based on our personal tastes.
Don't get me wrong, I know my post sounds a lot more negative about the WS than I mean it to be. We do enjoy it, but only to a degree which is probably less than some others. So for a family with young kids, I'd definitely ask if the things it has to offer are the style the kids and parents like.