My son will be 4 on halloween, and we haven't experienced this yet... which actually surprises me because neither his dad nor I wear underwear.
Tags on clothes really bother my kiddo, so the couple times he chose not to wear underwear, he was not real happy with the tag scratching his bottom. However, if he ever decided to not wear it anymore, I don't think I would particularly care. I think underwear was kind of designed to protect clothes during a time where they didn't wash their clothes as often as we do now (yay washing machines!) so as long as clothes are kept clean, why bother?
Just my opinion, of course.
FWIW, the times he didn't wear underwear, they never said anything to me at his school. I don't even know if they noticed.
Tags on clothes really bother my kiddo, so the couple times he chose not to wear underwear, he was not real happy with the tag scratching his bottom. However, if he ever decided to not wear it anymore, I don't think I would particularly care. I think underwear was kind of designed to protect clothes during a time where they didn't wash their clothes as often as we do now (yay washing machines!) so as long as clothes are kept clean, why bother?

FWIW, the times he didn't wear underwear, they never said anything to me at his school. I don't even know if they noticed.