Hi ,

The answer is never. You never retract the foreskin. It is like a finger just wash it. It self cleans and will retract when it's ready to. It can cause infection and be very painfully if you retract it when it's not ready as the skin is still fused to the penis.
http://www.kindredcommunity.com/arti...actions/p/1253

It will retract when it's ready by your son exploring himself.

Xx