If books were food, Berg's latest (The Pull of the Moon, 1996; Range of Motion, 1995; etc.) might be a Twinkie: the sweet tale of a precocious 13-year-old girl who falls in love with--and loses--an older man. Katie has had some hard knocks lately: Her mother recently died; her older sister Diane has gone off (pregnant) to Mexico to marry Dickie; and Katie has had to move from Texas to Missouri, where not only does she know nobody, but the two kids across the street are incorrigibly mean. Things quickly start looking rosier, though, as Ginger, the nice young woman who housekeeps for Katie and her dad, starts thinking that dad is more than just nice--even if he hardly ever smiles, which is only because he's an Army colonel. At school, Katie befriends the glamorous Taylor Sinn (a model), who turns out to be too fast with boys (Katie hates that) and a shoplifter. Katie has better luck with wallflower Cynthia O'Connell, who's slow at the start but steadily gains in true depth--and who has a colorful Italian grandmother who's dying slowly but just loves Katie. The big test, though, is when Katie falls in love with Jimmy, the handsome, sensitive--and married--Mobile station attendant ten years her senior who gives her a change of clothes after an ice-skating accident. There's real affection between the two, but the actual love is one-sided, and when Katie at last finds this out she's demolished enough to decide ""Well, I do not need love, I am just going to be a poet."" Good enough, but if Katie still says of Taylor's artist mother that she ""does gigantic paintings that you don't know what is,"" she may have to improve her language skills until she's at least 14. A pleasant between-meals snack of the kids-are-great genre: teary, funny, Hallmarkian wise, its tree space waiting among the YAs.