It is a beautiful summer day, and little bunny Karlchen is celebrating his fifth birthday! Well, that was the plan, but Karlchen's little sister Klara gets sick, and his parents have to take her to the doctor. The birthday picnic by the lake has to be postponed. Karlchen is disappointed and decides on a whim to move in with his Grandma. He packs his stuffed animals, Teddy, Dog, and Penguin, into the wagon and sets off for Grandma Nickel's house. However, along the way, Karlchen takes a wrong turn and ends up in the woods. Luckily, his kindergarten friend Monika, along with her dog Bello, has followed his trail. Together, they continue on their journey. A day full of adventures begins, and thanks to Karlchen's courage and resourcefulness, as well as his homemade birthday horn, there is still a big celebration in Grandma's garden at the end, complete with wonderful gifts and carrot cake with icing.