Jonni is a supporting protagonist in Little Brother Big Trouble: A Christmas Adventure. He is the son of Lenni, the step-son of Oona, the step-brother of Niko and the step-grandson of Grandpa. He was voiced by Juhana Vaittinen.
Jonni is a young innocent reindeer boy who unlike his father Lenni does not have any problems regarding the social aspects of life. The world is open for Jonni to explore and his childlike charm ensures that he can befriend anyone he meets. As an only child Jonni is always searching for friends and companions. He dreams of having a family - and a big brother like Niko, whom he truly admires.