I don't use TikTok (and based on some of their other actions, I wouldn't want to defend them), but I've just checked and their relevant terms of service appear to be:
Minimum user age 13, and anyone under 18 needs parental consent.
Don't see how a 12 year old should have any case against them. Another case of someone circumventing the rules and later on getting upset that they were allowed to. I feel that this is another attempt by the Children's Commissioner to force mandatory age checks (that cannot be lied to) everywhere online.