Baikinman turns Anpanman and friends into babies by using the red water from a mysterious fountain that turns anyone who touches it into a baby. 
 
Some sources list the movie having 3 episodes that total of 30min

One night, a Star of Life falls down the chimney of a bakery nestled deep in the forest, causing the dough in the oven to come to life. The dough becomes Anpanman, a superhero made of anpan (a sweet roll with bean jam filling). Together with his friends, Anpanman fights his rival Baikinman and helps the malnourished.
 
(Source: Anime News Network)

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