Thanks to Mud Pie's 2nd grade teacher, I discovered Symbaloo. Which is really nothing more than a cross-user, cross-platform version of Safari's "Top Sites" start page. Well, ok, it is more than Top Sites, because with Symbaloo I can make a webmix (or mix of bookmarked sites - that's visual rather than a pulldown list), and I can put it as the homepage for each of the kiddos. What's more, they can each have their own customized homepage!
I can put Dance Mat Typing and Starfall on Mud Pie's, Spelling City and TimeMaps on Fish's, and National Geographic and Kitchen Chemistry on St. Nick's. Along with about three dozen more - each. Each kiddo can have a customized background, too. Even Rowdy has a home page, though there's not much on it since she'd rather eat the mouse than click it.
Solved is the problem of Fish starting up the computer, clicking Firefox, and surfing away to Gamezone or some other time-waste site. Solved is the problem of finding a great educational link, emailing it to myself, losing the email beneath a zillion others, and forgetting about it entirely. I can add and delete links at will from my computer - no more logging on to the Family Dinosaur to change up the kids' home pages or nagging St. Nick to visit such-and-such site. Any changes made from the master webmix will be reflected on any computer where that webmix is displayed! How cool is that? What a fabulous educational resource!