I also think there should be a 'no' answer for the second question. (And maybe a 'what the heck, it's for charity' ;)

The fairy tales themselves are, by their nature, aimed at a young audience. The notes are aimed more at detail-obsessed fans, and imo are less aimed at children than the schoolbooks, because JKR can go into more detail about people and spells we know from canon, now that she no longer has to be spoiler-conscious. So to me it felt less jokey overall than the schoolbooks, though that could just have been the frame of mind in which I was reading.

More detailed comments on my LJ, if that may help you decide.