You know how difficult it is to get good photos of children. They fidget. They cry. And just when you think you've got the perfect shot, they turn the other way. Now try to imagine how challenging it must have been for early photographers, who had to contend with exposure times of minutes rather than fractions of a second.

A new exhibition at the Tokyo Metropolitan Museum of Photography not only reveals the tricks used in the first decades of photography to keep young clients still, but also explains the rapid advances in photographic technology during the 19th and early 20th centuries by focusing on that trickiest of subjects: the child.

The current show, in the museum's third-floor gallery through Sept. 19, is the second in a three-part series on photographs of children from the museum's collection of more than 25,000 works. Since this installment coincides with the school summer vacation, museum staff designed things to be relatively kid-friendly. Children under 12 are admitted free, and every Friday from 3 to 6 p.m. is designated as "Oshaberi Kansho Taimu," a time when visitors can talk freely without worrying about making too much noise. The exhibition will still be more interesting to adults, but a hands-on feature at the end, and the fact that most of the photographs are of children, makes this a nice opportunity for adults to share their interest in photography with school-age children.