They don't have to actually go indoors to have a baby. Check the population number (say its 30) then get a male and a female and keep on putting one on top of the other, but don't let them go indoors or anywhere. If you just keep placing one on top of the other, the number will eventually switch to 31, and a baby will suddenly appear in the female's arms. No need to wait for them to go indoors and even then they might not be successful so why waste that time? Just keep on placing one on top of each other over and over and over and over and over again until you see a baby in the female's arms.