Some animals can be bred with certain items. Hold the correct item and look at an animal. Then press the use button while still looking at it. This will cause love hearts to appear over it. This, sadly, does not mean it loves you. It means that it's in love mode, which is when it is ready to breed. Feed another nearby animal of the same type, and they will create a baby version of that mob.

Most babies grow up in around ten minutes. Some, like baby zombies, don't grow up at all.

Turtles can breed, but lay eggs instead of giving birth, much like real turtles. Chickens lay eggs every now and again and can give birth from breeding, unlike real chickens, which do not give birth to live young.