I'm not sure that's the consensus definition of whataboutism, despite it containing the key phrase. Whataboutism is generally of the form "Let's stop talking about X because Y is more important", which become a simple "What about Y?" "What about the children?" is generally used to support restrictions and might be used as a counterargument against things like the general availabilty of youtube but it's not usually used as an attempt to move away from the argument in question entirely.

I agree that we're wildly inconsistent about when children are treated as children, when they're treated as adults and when they become adults (16? 18? 21? when their brain development actually finishes somewhere between 20 and 30?). And not only do we end up with garbage laws but we also end up w garbage exceptions like in juvenile criminal law. We acknowledge that young offenders can't be treated the same as adult offenders because our legal system takes into account intent and the offender's ability to reason and know right from wrong, but then we charge children as adults when we're particularly grossed out by the crime or the prosecutor wants to appear tough.