Users under the age of 13 years

Instagram, Snapchat etc. Terms of Service state that they do not allow any users under the age of 13 years, yet their platforms are flooded with young children.

My Question: In a web or mobile app for users under the age of 13 years, how can I design a verification flow that allows me to obtain "verifiable parental consent" in accordance with the US COPPA and EU GDPR laws?

I am aware that I can request the parent to provide their credit card information, which I believe will count as "verifiable parental consent". However, I am wondering if there are other options with a lower potential bounce-rate?

If this seems "too broad" a question, I am specifically looking for a verification flow that allows the parent to choose from different verification options. A flow chart would be great!