I’m guessing your kids are a bit too young to have enjoyed BabySmash: colored blocks and sounds that changed and moved with any pressure on the keyboard. We worried that too much exposure would induce some kind of odd Pavlovian response or imprinting, compelling violent, fist-based enthusiasm at the sight of any laptop, so we tried to keep this balanced with healthy doses of, um, passive television viewing (well, Sesame Street). We’ve also found that older kids can basically hypnotize themselves flying around in Google Earth. If yours ever get interested, you might want to make sure they buckle into the chair…
Seriously, in terms of spending a lot of time on building a platform, it was our experience that the interfaces and the children and the interests change so fast, it was/is mostly easier to be accessible as a guide to scaffold, as you mention at the outset, rather than to build something time-consuming and temporary; better conversation opportunities, too, for things that are hard to anticipate—kind of an ongoing user-research environment. (I know you’re not abandoning anyone to the internet wilds, and your options are more sophisticated than my older observations—it’s just a two-cent comment.:-) ) In any case, the idea of modeling PLE processes at home is huge, as schools are slower in coming to grips with this. Fostering healthy PLEs for kids (both on and offline) does create a whole different mindset in terms of self-sufficiency, communication, and frames of reference for them. It’ll be interesting to see where they take us.