People generally do what’s easiest. Have you made it easy for them to include you, or easy for them to exclude you?
No judgement and no significance meant - I’m a peripheral school gate parent too
but I have enough friendly mums to chat to now and again and I don’t worry about the rest of it.
These WhatsApp groups aren’t started by someone diligently looking at the list of mobile numbers the school sends out. They’re started informally, bit by bit, and added to. I asked to be added to one last year and was included with a smile. It wasn’t a big deal. And it didn’t change much really!
If you keep your distance from them, they are merely maintaining it.
What I’m saying is: I understand your feelings of exclusion and I battle with those feelings sometimes, in general. But we have to take responsibility for how we come across to others and the reality we create.
If you don’t hang around chatting and you feel different to them (very aware of age difference) then you are a big part of why you’re not included. Again no judgement - I relate.
You can make changes - be actively friendly/approach for chats/ask to be included: “Hey, I’d love to be a part of the mums WhatsApp group, is it ok to add me?”
They are doing what’s easiest, and you can mold things to be more as you wish.
If they actively tell you no or snub you repeatedly then I guess they’re not worth bothering with but yeah, most people do what’s easiest.