My DD was 10 when she started. I don’t think I informed school (she’s 13 now), but I think I did ask her if she wanted me to let her teacher know so that she could have extra breaks etc and she said no. She took a pencil case with her own sanitary products in it and wore clothes with pockets for subtly transporting to the bathroom. I made sure she always had plenty in there so she was never stuck for them.
I suffer from a lot of symptoms, including pain too, so I was worried about the same. DD isn’t affected as much, although she’s slightly anaemic and has to take iron tablets. She gets headachy and sometimes a sore back, for which I give her paracetamol, but that didn’t start till around a year after she started her period.
At first she took it really well, I was quite shocked, but over time she started to have issues with san pro and wouldn’t use it, which eventually came to a head, when she broke down and asked me if there was anything that could just make her periods stop. We had a heart to heart, she changed products and since then she’s been absolutely fine (albeit quite moody when she’s on them!!). If I could go back, I’d have given her more options for san pro to start off with instead of just pads or nothing, I feel bad about that.
It can be quite a difficult thing for them to deal with when they are younger I think, but overall it hasn’t affected DD so much that she’s still struggling with it.