Like you, when I went with my parents, we would simply casually stroll the the WS, stop for lunch ath the American Pavillion counter service.....hit the rides at Mexico and Norway and catch the show in the American Pavillion. It never took us over a couple of hours.
Back in 2001, on DH & I's first trip together I set aside a half day just for WS, we saw a little more, but I still felt I was missing something.
This past summer I set aside one entire day just for WS. We made sure to eat lunch and supper in the restaurants. I got ahold of an entertainment schedule in advance and made sure we saw some type of entertainment in every country. We sampled different "snack foods" in each country as well. We took the time to walk through the exhibits and appreciate each one. It more than filled up our day. We also caught the ToD & Illuminations in the evening.
If you are worried about your children enjoying it, why not have them get the WS passport. They may be too old for the masks, but the passport is really interesting and a souvenier I enjoyed as an adult. One of the CM's in each country will write a message to your children in their native language and then let them know what it means. Or what about a fairly inexpensive souvenier from each country. I know my DH enjoyed trying on hats from each country (and the pictures I have are hilarious).
If you take time to enjoy the WS, and not just set out for the "major attractions" I think your family will really enjoy your time in this part of the park.