While there are episodes focusing on his younger years, like "Ken 10" which shows Ben as a 10-year-old, or the episode where Ben gets shrunk to a tiny size, there is no episode where Ben is depicted as a baby.
It's possible you're thinking of something else, or maybe you're referring to a fan-made creation. If you could provide more details about the episode or scene you're remembering, I might be able to help further!