When writing queries for chapter books, is it a good idea to mention "series potential" or plans for subsequent books? I know mentioning sequels when querying MG or YA novels is generally frowned upon, but with chapter books, it seems series are very popular.It's the same for books of all kinds. Series are very popular-- with readers, with publishers, with authors. Everybody likes a series, because it takes some of the tough decision-making out of reading / publishing / writing, and once they get going, series give you a pretty good return on your money / effort.
"Oh!" you say. "Well then why isn't everything a series?"
[Here we pause to let my readers consider this question for themselves.]
One possible answer is that the author didn't / doesn't want the book to be a series; he/she feels it's complete in itself and doesn't see a way to continue the story past what's already been said.
But the real answer is: not everything is popular enough to be a series. Sorry.
If Twilight had had a readership of 5,000, there would have been no New Moon, Eclipse or Breaking Dawn.
The reason editors don't want to hear about the author's thoughts on their book's series potential is for the same reason we don't want to hear about the author's thoughts on the possibility of getting their book on Oprah: AUTHORS HAVE NO CLUE.
More than that, experience has proven to most editors that the authors who are all excited about writing a series are either:
a) people who are under delusions of the millions of dollars there are to be made in children's books and who are uninterested in the quality of their writing in their pursuit of those dollars, or
b) people who are unhealthily obsessed with their creation and whose last interaction with reality was passing it in the street months ago, when they couldn't quite place where they knew reality from. It looked familiar... did its name start with an "R," maybe, or a "D"?
So we worry that if you've been spending a bunch of time over-enthusiastically plotting out the further adventures of your book, you haven't been spending a bunch of time making your first book the best book it can be.
Write the best book you can. The best book-- one book. If the editor sees the potential for great popularity and the beginnings of a series, she'll suggest the series to you.
UPDATE: Michael reminds me that some types of series (like his Animorphs) are pitched as a series, but as he also points out, that kind of writer can come up with a really catchy idea and churn out a hell of a lot of consistent prose over an extended amount of time (54 books in 5 years, for instance). As I've reminded him, that's not most writers.