Is it any easier or harder to edit a sequel than the first book?Different books present different challenges and with a sequel, a series or a companion piece, there is a little added challenge in that it's important to ensure continuity across all of the installments. In my experience, though, authors get to know their characters and setting so well in series that the first drafts of second and third installments are often stronger than early drafts of the first book. Perhaps editors of George R R Martin-esque sagas would give you a very different answer, though!
As a children’s book editor / publisher, do you have a time frame in which to publish a sequel for it still to appeal to the readers of the first book?When it comes to big commercial 'continuities' - like the Twilight series, say - it's a case of the sooner the better. The idea is that you want to catch the readers who loved the first book, and because children grow up so quickly, you really do have to move fast. We publish series such as Tom Palmer's Rugby Academy in this way to create anticipation and excitement - in that case we published installments every six months, and publication dates were linked to rugby seasons.
On the other hand a later sequel can give the original book a new lease of life and introduce it to a new generation of readers. An extreme example of that is To Kill a Mockingbird, sales of which are apparently up 6600% since the publication of the sequel was announced.
Why do you think children/teens like sequels so much?I think it's human nature to want more of something we love, and that's even more true of children, who are in a learning-heavy phase of development and can really benefit from revisiting familiar content. That's why young children love to return to the same book over and over again. With a series, the first book does the hard work of introducing the characters, setting and so on, and future installments can take the story and the characters further and further. Think Discworld, where Granny Weatherwax starts out as a minor character and becomes a force of nature.
I do think there's a danger that commercial considerations can result in slender ideas being overstretched by sequels that are unnecessary in creative terms. For my money The Hunger Games is an example of a book that didn't really need two sequels, and I don't think she's really in control of the sequels to the same degree. And personally I hate books like Mrs De Winter or Death Comes to Pemberley that take a gorgeous novel and try to weave in a sequel that necessitates untying the ends the novel has neatly tied up. It's like a published version of the sort of online fan-fiction that needs to know what happens in the bedroom between Jane Eyre and Rochester. Although speaking of them, Wide Sargasso Sea is an example of a very good revisiting because it challenges the very fabric of the original. Maybe that's the key to those sort of sequels - you can't love the original too much.