Minecraft wiki entry for Legacy_village_mechanics, associated text: Residents of a village that has not yet reached its population cap occasionally go into "love mode," indicated by animated hearts above their head (only visible if you have particle effects enabled, but still works even when you can't see it working). Much like with farm animals, when two villagers are feeling "romantic" and can see each other, they pathfind towards the other and "kiss" for a few seconds, after which a third, smaller ("baby") villager spawns next to them. This new villager gets assigned a random profession (indicated by the style and color of its clothing), not necessarily the same as either parent.