-Place a male on a female, or vice versa. The message "Going indoors for some privacy" will appear. Move the male villager from his place. You will see a baby in the hand of the female villager.
-You can tell if the couple who are going indoors will make a baby or not because the population will change as soon as they say "Going indoors". If they are not going to make a baby, pick them up and try again instead of waiting for them walk over to the house. You also do not have to wait if they are going to have a baby. As soon as you see the population change, pick up the female and the baby will appear in her arms when you put her down.