The two theories I see for the etymology of "googly eyes" are (1) that the term descends from goggle + -y ( https://www.etymonline.com/word/googly ); or (2) that the term is related to a comic strip character named Barney Google ( https://blog.retroplanet.com/googly-eyes/ ). Neither theory involves a -ly suffix.

They don't really involve the diminutive -y suffix either; that looks more like the adjective-forming -y suffix.