1798.503(b) An operating system provider or a covered application store that makes a good faith effort to comply with this title, taking into consideration available technology and any reasonable technical limitations or outages, shall not be liable for an erroneous signal indicating a user’s age range or any conduct by a developer that receives a signal indicating a user’s age range.
OR instead of having to collect that info at all you just put "OS not for cali" on the user agreement and just not deal with the risk.