I have little grandson (5 month old) who has been circumcised. His little penis goes back into his scrotom but when you push on the side it pops out again and as soon as you take you hands away it reseeds back into the scrotom.
I think you will find this is normal but I suggest that his mom or your self ask the Doctor to make sure ...its because he is so young ...as he grows I think it solves itself ..good luck