Cute as a button (also used as cute as a bug’s ear) simply means “cute”, only in a more informal way.
The expression is an idiom, meaning something is appealing or charming in an elegant way, and is often used in relation with little children or pets, that show resemblance in size proportion to a small button.
The word “cute” stems from another expression, “acute”, which means clever or witty. The word eventually gained its own meaning during the 19th century.
The expression cute as a button came to existence somewhere during the 1920s, when “cute” and “keen” were two of the most highly popular slang words in American-English.
Cute as a button is still commonly used as an idiom in informal English to this day. It is usually featured on various media platforms that target young children as an audience.
The expression got featured during an episode of TV cartoon series American Dad, appearing as a song title that is performed by the character Reginald.