Or, in the spirit of the story, ""Ivy and May Strike Back"": they don't like to be thought of as one, called ""the twins,"" or treated like freaks. It's a situation that other youngsters, twins or not, can sympathize with, though one somewhat advanced--Ivy and May are eight--for the picture-book format. And the way the twins work it out--via an elaborate ruse--might also baffle anyone below, say, the second grade. Still, given the built-in limitations, this is worth having around. To get back at big sister Bernadine and older cousin Nate (""Well, well, well, if it isn't Pete. . . and Repeat,"" etc.), Ivy and May decide to pretend that they really do know what's in each other's mind. By prearrangement, May disappears when Bernadine and Nate are in charge; they are reduced to begging Ivy to locate her; and Ivy leads them from one locale to another, minutes behind May, until all the children wind up at their grandparents (for the twins' birthday celebration) where Bernadine and Nate, chastised, are properly contrite and Ivy and May are undisguisedly exultant. Strong feelings, openly displayed, are one attraction of the pictures of the (black) children too.