It's always fun in Bullerbü, but when Lasse, Bosse, Lisa, Britta, Inga and Ole decide to arrange a Children's Day for Ole's little sister Kerstin, it's even more fun than usual. That's because Kerstin has her own ideas of what is fun, and doesn't want to do the same as the big children. They have to come up with lots of ideas so that Kerstin can also enjoy Children's Day ...