This is the sort of benign fancy--contrived out of other children's books, and ideas of children's books--that goes down easily but fades as quickly. August Brown, ten, has just moved from Vermont to Georgetown, because his newly-divorced lawyer mother has a Washington, D.C., job. In the usual doldrums, and prey to the usual suspicions of a sour-faced boy on the block, August impulsively follows the local bag-lady . . . into Pineapple Place, a picturesque alley populated by animated kids (and adult eccentrics) who've been together intact since 1939. (Then, Pineapple Place was in Baltimore; for fear of the war, Mr. Sweeney, one of the resident gents, moved it to Phoenix; now he shifts it about periodically.) Ordinarily, Pineapple Place and its denizens are invisible--save for bag-lady Mrs. Pettylittle, whose scrounging keeps everyone supplied. So August has a hard time explaining his jaunts with congenial age-mate April Anderson, and the others; his mother thinks he's made up invisible friends out of loneliness. Various invisible-children-in-Washington escapades ensue (disporting in a White House pool, roller-skating in the National Gallery), with August meanwhile coming to realize that his mother's entitled to work (and isn't neglecting him). And before she and Pineapple Place leave, April arranges that he meet that sour-faced boy on the block--who turns out of course to be a good sort. None of this is original or especially engrossing--but it does avoid the excesses of much celebrity-writing for kids.