I haven't started one yet, because they really don't use the computer a lot, much less the Internet; but we've found some activities that we really like (for school, rewards, communication) and are planning to integrate them into our daily lives a little more this summer. Among the possibilities, I'm sure a Lego link is going to top the list, and we're beginning an online tutoring program called ALEKS for math with at least one of the kids in the next few weeks. I'll have to experiment with my school bookmarks a little to see what else will work.
Do you have any favorite web sites for kids? What would be at your online portal?