GoldenHermit

According to the guide, breeding animals can only be done trough feeding them with a trough etc. But I've seen all sorts of animals with a baby around like chickens, wolves , hares and boars. Do they simple spawn that way (male, female and a young) or not? I'm wondering because if they don't simply spawn like that, would it mean I could fence them in a large area and expect to see a lot of chickens ... eventually?