My DD (9) loves World Showcase. We spend more time there than in FW. The Agent P adventures are one of her favorite things at WDW. She also loves the character meet and greets, the entertainers, the boat ride in Mexico, the movies about different countries and looking through all the shops. She liked the Kidcot stations when she was younger, but she has outgrown those; however, if your child has not done the KidCot stations before at her age, if you buy her one of the passports, it might be fun for her to go to the Kidcot station in each country and get it stamped.
What we do is start at rope drop in FW. The first day we usually do everything we can on the Soarin side of the park. Then we typically go over for a TS lunch at WS at 12:00 or 12:30 (unless it is Food &Wine, then we head over right at 11 to hit the booths which are less crowded earlier in the day - doesn't Flower and Garden have some food booths now?). We rarely make it to the other side of FW before moving over to WS, except now with FP+- we trek over there if we have something set up there- usually Mission Space when it was not Tier One. Biergarten is a must do TS for DH and DD at least one of the days (during Food &Wine- we will do that for dinner while the booths are crowded instead of at lunch). Once we are finished with TS lunch, we go to one end of WS, usually Mexico, and start working our way around (if it is Food and Wine- then we just start hitting the booths at 11:00 a.m. on the Mexico end and start working around). We almost never make it all the way through WS by closing even starting that early as DD just really loves that side of the park. Our 2nd day, we start back in FW and do the same thing- but we will either start WS where we left off or at the other end working toward where we left off. FW, we start on the Test Track side that morning typically and try to catch everything we did not do the first day- but DD usually does want to go back and hit FW things on the other side a little bit too. We have been going with DD every year since she was 2, and because she loves WS and wants to spend most of the time there, even with 2 days, we have yet to find the 45 minutes to do Ellen's Energy Adventure! When she was little, we didn't do it because we were worried she would suddenly need a bathroom break during the 45 minute ride and it would be bad- now we just never seem to find the time.
We don't do afternoon breaks. For us, we just lose too much time in the day. We get our rest break by either doing the TS lunch, sitting down and having a snack in WS, or by sitting in American Adventure or one of the movies that has seats. Ellen's Energy Adventure would make for a good break, but we never seem to make it back to the FW side once we have moved over to WS.