that your son and these girls are going to have sex, not their safety.
You should not worry about this. Your son and these girls are not stupit as you may think. They may be very inteligent and smart kids. They know what they are doing. they may be more intelligent and smart than you. do not worry about them.
it is not your business at all. You should stop doing or learn to stop doing this. it is good for your son and it is good for you too.