R.L.
No a circumcision can not reverse itself because they actually remove the skin. Most likely this is just due to regular growth and he will eventually grow into his skin.
It is very important to keep the area clean. It is completely normal for white gunk to build up, but if not cleaned properly (by pulling the skin down and washing with mild soap and a washcloth) then it can lead to irritation and infection.
Sometimes a small skin tag will develop and cause the skin to bunch up. At your next pediatrician appt just have the doc take a look. Most often skin tags will break on their own as he grows, but sometimes they need to be broken by the doctor.
I had a similar experience with my son, he's 8 now and every thing is growing and looking just fine!