Your kittens will run the risk of getting infected with this virus if they catch and kill a mouse carrying it. I do not know if there is even a vaccine for cats to safeguard against this? Try sealing up all the cracks in your home, repair torn screens if any and try to keep the mice out. Remove any stacks of wood near the house, piles of newspaper, whatever a mouse can find to live under and feel safe. If one of your kittens brings you a dead mouse, dispose of the mouse with rubber gloves and put the rodent into a baggie and seal it up before either throwing it out or burning it. But again, you run the risk of your kittens catching this virus. Most cats hunt by instinct, feral kittens are veracious hunters at about 2 months old and females make better mousers then males. You also might want to watch out once they start killing the mice for parasites in your kittens.