Ooh, we did the book advent calendar two years ago! It can get a little expensive, so every second day I substituted in some second-hand magazines that DS enjoyed, which I had bought second-hand at about 10 cents per issue.
RRD--have you tried the "Notebook of Doom" series yet? Or "Data Set"?
I have a few decent sources for used books, so I got a mix to bring down the cost a bit. And yes, we've tried the Notebook of Doom and though they liked it, they found it a bit too scary. We've been working on it, but they get scared at the slightest thing in books or tv/movies. Haven't tried Data Set yet, but it would probably be well-received.
And by the way, the books have been a huge success! DS6 (almost 7) announced that he preferred the book advent calendar over the Lego City advent calendar. I almost got teary, I was so happy.
As for the suggestions for gift ideas, they're all terrific. I particularly love the Engineering Gift Guide. And that reminds me, DS6 has been engrossed in their Snap Circuits Jr set for the past week and has been whipping things together without looking at the instructions. Maybe it's time to get them a more advanced set!
