AFAIK COPPA is for the site's data collection, for example, the site collecting marketing and demographic and PII, that you can't opt out of and that the child

AFAIK COPPA is for the site's data collection, for example, the site collecting marketing and demographic and PII, that you can't opt out of and that the child does not understand. Your child sharing personal information of their own accord shouldn't be covered by this.