When we went in 2004, my kids were 2, 6, & 8. They hated it and we had to take them out. It sort of ruined the rest of the 3D movies that year. None of the kids wanted to go to any of the "movies".
We went last year and did not attempt It's Tough To Be A Bug. We WILL be going next year. Kids will be 7, 10 & 12. They better like it then. They liked the other 3D movies last year.
My suggestion is to work up to it. Try Philharmagic. Then maybe the Shrinking movie at Epcot (for the life of me, I cannot think of the name...) Then if they like those, they will probably be okay during the Bug one. It will be dark at times, so make sure they are prepared.