My teens keep turning into vampires

Since starting up the game today sometimes when my teens travel out of the house they turn into vamps with the thirst need red.  Discovered this when he traveled for the prom (Glad its back) but arrived as a vamp that was very thirsty.  I switched to his brother and then back to him a few minutes later and he had switched back but its happened a few other times since then with other houses and I had to go to CAS to fix them.  I have no clue what to even tag this as