13 turning 14 soon. He doesn't have WhatsApp as he's never "needed" it before. However, now he has a friend who wants him to use it rather than sms. (DS has ASD and basically never had friends before).
I've no idea if there's a class chat or whatever as it's never been an issue before.
External clubs all have a WhatsApp group but I sort this for him through my phone, most children seem to be on the group as well as one or both parents.
DH is very anti WhatsApp, doesn't have it and doesn't see the need for the DC to have it either.