Welcome and thanks for posting your query to HCM.
As per the history given by you it is quite early to comment on the problem of your son at the age of 12 years ( even below teenage !!). At the age of 12 years there is less of orientation towards opposite sex but you should not forget that this is the the tender age where the orientation actually starts. As you said you saw them sleeping naked together but not actually doing anything, makes a bit of the sense of going in wrong direction. Though it might be a part of simple curiosity and experimentation but even then it's my personal suggestion to you to keep a watch. If you see the repetition then talk to your son taking him in your confidence. Still after this if you see something illicit then it would be the best thing for your son to get proper counseling by Psychiatrist
. After all he is your son and should not leave the problem leaving like a simple matter of choice !!
Hope to give you the best of the information.
With best health wishes,
Dr Sanjay K Kanodia
MD ( Dermatology and STD/ Venereology)