From the Super Mario Wiki, the Mario encyclopedia

I always thought the name resembled the word "mild", as these enemies are very mild-mannered, and don't pose much of a threat. -- Son of Suns

I always thought that kirby and the mildes were related because they looked so similar.
The preceding unsigned comment was added by Xxxzzz1 (talk).

No, they are not. Don't add it in without proof. Ashley pose SMM.png Mario JC