A mobile -- of patterns, forms, forces within the circumference of life-with-young-children in a small New York city apartment never moving any further away from it than the park. Sonya is a photographer devoting her weekends to right angles when Victor, an ex-ski bum, moves in and then she devotes herself to him and to two infants in rapid succession. Parkbench and sandbox scenes alternate with her crimped and cluttered life within the shrinking apartment -- the damp rounds of child care -- the splintered privacy (""Look at Rose Kennedy. She never complained."" -- that's Victor -- he gets away from it). The book, like her life, is an eidetic reprise of ""bodies in motion,"" touching here, drifting away there, ""the one with the greater mass winning the tug of war."" That will of course be Victor again. . . . Perishable perhaps, but weightless, lucent and charming.