people take mi baby (visitors!)

i have a baby and everything's fine, i feed it, play everything!! then my sims'es son brings home a friend and she holds the baby and a bubble comes about her head (the hunger one) and she just walks away!!!!!!! (out of my lot) and the baby isn't listed under my sims any more? this has happened twice! i dont know what to do, last time i saved, exited and came on but the baby was just outside my lot, i could see it but not pick it up, i lost the baby please help i dont want it to happen again :(