When I was messing around in my world I decided to spawn in a baby villager using commands,when I put in the command and the event string and executed the command it spawned in a nitwit,then I did it again and that time it gave me a farmer,I then tried all the other event strings for the villagers,every time I put in a string the game ignored it and just spawned in a random villager,I even checked to make sure I put it in right even if it was done correctly the game would ignore it,as you can see in the image below,I entered the event string for a baby villager,but instead it spawned an adult villager that's a shepherd as well.