What did 9-year-old Milton Sirotta invent in 1938?

The word googol

Bingo! His uncle was Edward Kasner, a well-known American mathematician and educator. I first read about it in Mathematics And the Imagination by Kasner and Newman when I was about 12. Still on my shelf.

Googol is a synonym of ten duotrigintillion.

Did you search for the answer using its homophonic namesake?

Yeah, Professor, on Google.

Ah, excellent. Since the name "Google" was inspired by "googol," this is what author Douglas Hofstadter would call a strange loop of self-reference.

Thank you, Miss EOM!