kindly do not kill them. in todays newspaper you might have seen that rats are multiplying in industrial area and causing many diseases like plague etc. Most of the cats have vanished from the street. If you get time kindly give the waste of your food away from your house so that they will keep staying in that place instead of coming to your doorstep. Keep the food in a safer place and place some water so that they may remain some safe place nearby. I am doing the same thing.