That's not true. Consent is only one basis for processing. If they stick to using it for legitimate interest reasons then they don't need consent. Even ads can

That's not true. Consent is only one basis for processing. If they stick to using it for legitimate interest reasons then they don't need consent. Even ads can be a legitimate interest, and probably are in twitter's case, though the user is always allowed to opt out of that. There's also nothing that requires parental consent to involve signing a form.