With a bright idea and bundles of affable vibes, this dream-come-true adventure of a pint-sized con artist (as he calls himself) has lots of up-front appeal. Fatherless, ten-year-old Danny's MO is to hang around the Bronx Zoo on weekends, sidle up to one of the divorced ""zoodaddies"" on an outing with a son, winningly enter their conversation with information about the animals--and by then the zoodaddies are hooked. Danny is invited to a zoo lunch, a fantastic afternoon on the town, and a special dinner. . . perhaps in Chinatown, perhaps atop the World Trade Center, perhaps at home with a large Hispanic family who become his special friends. There are in fact several ""reruns,"" as he calls them, and several fond relationships. Danny has to buy a datebook to schedule his weekends. But there are always enough cancellations so that he can keep his skills in practice picking up stand-ins. Danny's cover is blown when he shares his secret with an almost accidental pickup, his first zoomommie; and she, a TV newscaster, brings him instant celebrity. Soon the local media dub him ""Son For a Day."" Far from feeling cheated, as Danny had feared, all his zoodaddies and zoobrothers get together for a party; and we leave Danny with his mother in Chicago. . . where the Museum of Science and Industry teems with daddies who haven't yet heard of Son For a Day. Simply as a sightseeing tour, this is worth the ride; then too, even if you don't get to know anyone that well, you meet all sorts of nice people.