Good luck - for a free library event surely it shouldn't be a big deal? I've signed up DD to slightly more formal science classes where the teacher allowed her in but expressed doubts and requested I stay too (parents could stay or not as they wished) in case she needed help.
She didn't
She completed the whole project completely by herself, first in the class - she was 7 in a class for 9-12 year olds. Teacher was impressed so hopefully we'll get in without question next time! (although honestly not sure how she'd feel about DD joining the 12-16 year old classes, which would actually be challenging for her, and I'm not sure how I'd feel about that either)
For casual things at the library I haven't even bothered specifying her age. Maybe bald-faced lie to them and say you made a mistake, he's really 10
