TRADITIONALLY, the big push for children's book publishers comes in the fall, when they release new titles for the holiday gift-giving season. But this spring and early summer have produced a bountiful yield of fun new picture books that are already beginning to hit the public library shelves.
* ''Greyling,'' by Jane Yolen, illustrated by David Ray (Philomel Books, $14.95, ages 3-8). The rich fantasy lore of Scotland includes tales of selchies, who are seals that transform into humans on land. In this retelling of a classic folktale, a fisherman and his wife are sad because they do not have a child.
One day the fisherman rescues an orphaned seal pup, who magically becomes Greyling, a baby boy with silvery hair and gray eyes. They adopt him, thrilled to have a son yet aware they will someday lose him, for all selchies must return to the sea. Greyling ultimately does, too, when he dives into the water to rescue his father from drowning and is transformed back into a seal. The seal visits the fisherman and his wife every year after that, ''to sing them songs of the wonders that lie far beneath the sea.''
Yolen, who teamed up with illustrator John Schoenherr to win the 1988 Caldecott Medal for ''Owl Moon,'' weaves words together beautifully. And Ray's acrylic paintings are soft and spooky. Parents will have a hard time making it through this story of loving and letting go without choking back a tear.
* Parents may have a harder time explaining ''Bear,'' by John Schoenherr (Philomel, $14.95, ages 4-8). Fans of ''Owl Moon,'' will be captivated Schoenherr's exquisite watercolor paintings of a bear cub lost in the Alaskan wilderness.
But it could be tough for a 5-year-old to cope with this story of abandonment and survival. The young bear wakes up one morning to find his mother gone. He searches their familiar trails and can't find her. He wanders aimless and hungry, gets chased by an angry mother moose and runs up a tree to escape an attack by an older bear.
Sure, that's nature, and nature is scary. There's a happy ending, as the starving young bear figures out how to catch salmon and eventually grows strong and fierce. But many a child will keep going back to the beginning, asking: ''But why did his mother leave him?'' That's never easy to explain to a kindergartner.
* ''Tuesday'' by David Wiesner (Clarion, $15.95, ages 5 and up). Buy this book. Anyone who is having a bad day -- whether it be a 7-year-old who flubbed a pop quiz in spelling or a 37-year-old whose employer keeps hinting that the recession will bring layoffs -- will get instant relief by picking up this book.
Wiesner's sense of humor and fantasy have to be seen to be believed. Try to imagine hundreds of frogs flying out of the sky on lily pads around 8 p.m. on a Tuesday night. They cruise past the window while you're eating at the kitchen table. They get snagged in the sheets left hanging overnight on the clothesline. As the night grows late, they float in through the window and down the chimney and hover 'round the TV, as one of them flicks the remote control with his tongue.
But such descriptions can't do Wiesner's surrealistic whimsy justice. And next Tuesday, at 7:58 p.m., an even more imposing flock of creatures soars through the sky. Ah, but that would be giving it away . . .
* Amphibians also win the day in ''The Frog Prince, Continued,'' by Jon Scieszka, paintings by Steve Johnson (Viking, $14.95, ages 4-9). Last year Scieszka captivated readers with ''The True Story of the Three Little Pigs,'' and he's done it again with this story of what really happened after the princess kissed the frog and turned him into a prince. They hardly lived happily ever after.
No, the princess nags the prince when his sticky tongue absent-mindedly darts out at the dragonflies on the wallpaper. ''First you keep me awake all night with your horrible, croaky snore,'' she tells him. ''Now I find a lily pad in your pocket. I can't believe I actually kissed your slimy frog lips. Sometimes I think we would both be better off if you were still a frog.''
The prince agrees. He sets off to find a witch who will reverse the spell, although it's not easy. The first witch he finds in the forest thinks he's out to save Sleeping Beauty. The second witch offers him a poisoned apple, straight out of Snow White. The third witch wants to add him to her menu, along with Hansel and Gretel.
Finally, after a botched rescue attempt by Cinderella's fairy godmother, the Frog Prince (positively frog-like with his skinny, springy legs and bulbous eyes) decides he would rather be at home with the princess, nagging and all. And she decides she missed him terribly while he was out running around, trying to turn back into a frog. So there's a happy reunion and an even more satisfying ending.