Becoming retractable involves two things; first is the dissolving of the natural adhesions that attach the foreskin to the glans, second is the loosening of the sphincter at the end of the foreskin. These can happen in either order, and any time between infancy and the completion of puberty. These happening at different times is most noticeable when the adhesion dissolve before the sphincter loosens and the foreskin balloons while peeing.
The breaking up of the adhesions also don't always happen completely all at once. Sometimes a small area of the glans and foreskin separate, but another spot will still be firmly attached. This can create little pockets where smegma builds up and forms a smegma pearl. This is normal and harmless.
Since there is a huge range of normal when it comes to retraction, so one twin may be completely retractable long before the other on even begins.
Occasionally there are some minor symptoms associated with separation. These include minor swelling and redness, ballooning, discomfort or pain while peeing, and smegma discharge. These should all clear up within 24-48 hrs, but may reoccur if a new area starts to separate.
When they are clearly fully retracting comfortably, you can instruct them to clean underneath with plain water no soap (just like with girls,) but it's not really important till puberty.
