What do you think the age ranges are for Bob the Builder, Thomas the Tank Engine, Disney Princess, and Hello Kitty toys/bedding/etc.? How old would a child be when he/she would outgrow each of these and no longer think they're cool?

My 2-year-old DS *loves* Bob the Builder. He has a toddler sheet/comforter set that's in the Bob the Builder theme, and we bought (on sale) a twin bed sheet/comforter set for him to use later. Now, though, I'm wondering about the twin bed set. He probably won't use that set until he's 4 or 5, and we'd like for him to use it for a few years. Do you think that Bob the Builder is popular among grade-school-age kids, or would Thomas the Tank Engine be more appropriate? (I'm trying to picture him as a second- or third-grader with Bob the Builder bedding. I wonder if he'd like it when he's that age. I'm pretty sure kids that age still play with Thomas stuff, so maybe that theme would be better.)

Also, does anyone know if either Disney Princess bedding or Hello Kitty bedding is popular for grade-school-aged girls? I'm thinking that my DD (DS's twin) would probably like Disney Princess bedding longer, but (thinking back to my grade school days) I remember having a friend who liked Hello Kitty stuff in the fifth grade. So maybe a third-grader would still like it? The Disney Princess bedding seems a little more elegant/grown-up, though.

Yeah, I know ... I have waaay too much time on my hands if I'm worrying about this, right? LOL! Maybe I should just return the twin bedding set and wait a couple of years, then see what my kids like.

Any advice would be appreciated, though! :)