How can you get your baby back from social services on the sims?

Sorry, but once the baby is gone and you save the game, there is no way for that family to get that baby back. Another family in that neighborhood can adopt it, and i suppose you could maneuver things so that the baby lives with its original family again, but the family will not "recognize" him/her as the same baby. If the social worker takes the baby, but then you exit without saving, when you came back to the lot you will be back to before the baby was taken. but unless you fix whatever situation caused the social worker to come, they will still come and take the baby away.