I knew about periods, from friends, and my older sister had them. Her used sanitary pads were put discreetly into our aga type burner, but it was all done with embarrassment.
I actually started at school when I was 13, I had some money but no three old pennies which was what you needed to buy a towel from the machine in the toilet. A friend and I went to the staff room, it was dinner time, my form teacher, a rather dishy young male teacher came to the door, I made some excuse as I was sure if I asked to change my money for pennies he would know why! (How idiotic, he was married with a baby).
A friend lent me the pennies, I bought a towel, feeling quite mature! When I got home, Mum rigged me up with what I needed but never really explained much. I always had a spare sanitary towel in my satchel from then.
I progressed to Tampax later on.
“No belts, no pins, no pads, no odour”.
Should say, things were obviously different with my own daughter. As for boys not knowing about such things, can remember being in Boots with DS when he was about 6, and he suddenly yelled across the shop, “Mum, do you need any Tampax?”.