Verified answer

Did you check the Family Bin? When you tell a sim to move out of a household and take a baby with her, she won't pick the baby up when walking to the taxi that arrives to take her away. So it would look like the baby is left behind, but in reality he would disappear shortly after the taxi leaves, and you would find him in the Family Bin with the adult Sim.

I'm not sure if that's how it works when Sims get pregnant in uni though. It would depend on the mod you use. Is this situation mentioned in the information provided with the mod?

If the baby is still in the student house, you could move in another Sim and try moving out again, hoping that this time the baby will move out with the adult. Then you can place this other sim in the neighborhood and move in the baby's mother with him.

Hope this works.