I would think trying to pass an id off on your 8 yr old could make it more difficult to claim they are your kid and need to be with you because it makes you look like a jackass trying to sneak them in. If they balk start shouting about age discrimination (against you not the kid) and the struggles of being a non traditional student. then ask if they are going to pay for daycare for your kid. they'll probably cry uncle somewhere in there.