We are happy to welcome you to the CAC and hope you stick around and learn why we tell everyone to not retract.
It can really hurt your child. While the foreskin is not made of glass and easily broken it can develop scar tissue causing major problems for the boy down the road. One of the reasons circ became such an issue here in the USA was the advice to retract at ever diaper change from birth. This lead to many boys who even after puberty where unable to retract due to the scar tissue. My older brother was one of those boys he "had" to be circed at 3yo because he got an infection and because he still wasnt retractable. Of course neither of those things is a reason to circ but my mom didnt know better just like she didnt know to leave it alone so my brother paid the price for it.
To understand why retraction can be so bad for a infant/young child you need to understand how the foreskin works. It is attached to the glans of the penis like the finger nail is to the nail bed and the tip is a sphincter like the anus. When not in use it clamps down to keep germs, poo and other things out. It only releases to let the urine pass. By forcing this sphincter open you can damage it causing scar tissue to form it can also cause micro tears that allow bacteria in. Like the anus no stretching is required and like the anus doing so can cause pain and issues down the road.
Another thing I want to point out by telling people they need to mess with their ds's penis so much it will really put people off keeping their ds intact because like me the idea of messing with their ds's penis that much really makes me uncomfortable. Just like it would if I would had to mess with my dd's genitals that much. It also lends credence to the myth that the intact penis is more work than the circed one when that isnt the case at all. Like the vagina the intact penis is self cleaning, if you where to constantly clean inside your vagina you would have issues just like you will have issues by over cleaning of the intact one. Especially one that isnt retractable yet.
Think about it this way. We dont have to "train" other parts of the body either male or female to do their job so why would we need to do so with the foreskin? It dosnt add up.
It isnt necessary and it is potentially damaging. If it isnt ready to retract and you make it go back to far it could get stuck behind the glans and that is a major problem. I understand you said gentle manipulation but even that can cause problems simply because you cannot feel if it is hurting the child and by the time you know it did it is to late the damage is done.
The rule is no one but the owner of the penis should ever retract it. Starting when your ds is old enough to understand have him pull back as much as he is comfy with rinse with clear water and replace. Until he reaches puberty it isnt even necessary to do that but it is a good habit for him to get into. Before that you wipe like a finger only from base to tip and otherwise leave it alone and dont let anyone else mess with it. Here in the USA we have major problems with Dr.'s retracting the penis and causing harm on infants and young boys. You are lucky that you live somewhere that the Dr. know better.
I understand that you have had many members of your family who did this with no problem but odds are they would have became retractable when puberty hit like the body was designed to do and they wouldnt have had to deal with someone messing with their penis so much.