Baby villager(s) spawning when a villager of any profession becomes a Apprentice

I don't know if this is a feature or bug or it is just because of how many villagers are in my Minecraft Creative world, but this keeps happening when I trade. When I trade with a villager, when it becomes a novice, 1-2 babies just appear out of nowhere right where that villager is. Please note this only SOMETIMES happens.