Farfallina & Marcel by Holly Keller

A caterpillar and a baby gosling become fast friends.   But, one day, Farfallina the caterpillars climbs up a tree and doesn't come back down.  Marcel waits and waits for her to come back, and finally gives up.  When Farfallina finally does come back, she looks and looks for her friend Marcel, but only finds a grown up Goose, who also says he is missing his old friend.  They become friends, and finally realize they were missing each other.