I'm spit-balling here and could be way off. While it looks fairly safe to assume the baby is dead, I'm not 100% convinced, when those young girls shot the two folk, they ran the wrong way, the way from which they came and Tyrese told them they were going the wrong way and followed after them, now I don't know the full layout of the prison but I'm sure the carrier wouldn't have been hard to spot right out in the open and the kids were probably going to go back for the baby. Tyrese would have seen the baby and there's no way he would have left it behind, now I'd have to watch it again to see if he was covered in blood or not but after the fight there's a strong chance he was covered in blood and smeared the inside of the carrier. Walkers aren't smart enough to unbuckle the car seat and carry the baby away, if they did eat the baby then there would have been some sort of remains there at the very least. That said, I'm not saying the baby is alive or dead, I'm not sure of either. I'm just saying either the writers left some pretty big plot holes OR there's more to it than Judith being eaten by a walker.