How long should a chapter be?
Like so many writing related questions, my answer is: it depends.
Many contemporary thrillers seem to consist of literally hundreds of chapters, with each lasting no more than two pages. I am Pilgrim is a good recent example, and anyone familiar with the works of Michael Crichton will also know what I am talking about.
Other texts, surprisingly often stories aimed at children, contain chapters that at times seem very long. Harry Potter and the Order of the Phoenix contains many lengthy chapters, for example.
Both approaches work well for their respective formats – fast contemporary thriller, versus more traditional fairy tale. The short chapter approach doesn’t necessarily mean the writer considers the reader to have the attention span of goldfish. Other novels have a mixture of short and long chapters for artistic reasons – Life of Pi, for instance.
In my own writing, I generally stick to average length chapters in both my novels for children and for grown-ups, regardless of genre or subject matter. My stories seem to naturally gravitate to a relatively straightforward format. However, the stories themselves are often anything but.
On a related note, I generally do not title chapters in a novel aimed at grown-ups (with rare exceptions), but I always do in a novel aimed at children. Why? I have no idea. Perhaps chapter titles in books aimed at children just sound cool.