The more I thought about all this technology, and how my own three and five year-old sons use apps, the more I realised that the best children's apps are successful because of a pair of more traditional qualities.
Great storytelling. Strong characters.
It seems apps aren't so revolutionary after all, but that's a good thing. Treat any claims that apps are set to kill off books with the derision they deserve. Apps are just another form of storytelling, and one that sit alongside printed books rather than trying to replace them.
(This, hopefully, will head off the crotchety commenters who appear whenever I write about children's apps for The Guardian, saying things like "You idiot! Children should be reading BOOKS, not staring at a screen!" Ridiculous, since children in even the geekiest households are doing both, not replacing the former with the latter.)
Children love great stories and strong characters, whether they're on a screen or a printed page.