This is me and my eight year old, building on our OpenSim island:
She's enjoying it quite a lot, and learning fast as well. This object below her first build - I admit, I helped her with positioning the roof, the rest is her own work!
We're having fun as you can see, but we're also noticing the limits of this opensim alpha build. I had a client crash when saving a new outfit, and we have to select our clothing and body shape each time we login. But hey, it's alpha, I'm not complaining!