Okay, Then he was seen born at the end of AHS Season 1 (can’t remember if it’s the one before last, or the one even before), but we don’t see him grow up in that season :). We only see one scene from him being a toddler. The most we see of his chidhood is seen in Apocalypse.

Well it depends what you mean as him being a baby. Him being born, and the glimpse we had of him as a toddler was in Murder House the last 2 episodes (AHS Season 1).

In that season he always was perceived as an adult even though he was barely 5 (?). As I am French I haven’t seen the last few episodes yet :). But that’s what I got from the various spoilers.