Earlier quoted context omitted.
You ask the users for their date of birth on signup, don't tell them that it will be used for age-gating features (to avoid incentivizing lying), and don't allow the date to be changed without some kind of age verification. Or you use the social graph to infer age: somebody who mainly plays with 10 year olds is probably also about 10. If they claim to be 20, require an id anyway. Non-gaming companies deal with this a…
So are we all forced to have a signup at the start to not get sued? Can't just have a mobile/browser game that tracks basic data?
Yes, we all know kids lie when they see the age verification, but the presence of age verification moves the liability away from the developer/publisher and onto the parents/guardian of the underage kid.
Obligatory IANAL.