Yes kids should have to wear gym clothes
No kids should not have to wear gym clothes
wearing a specific outfit for pe makes it easier for the students to exercise if they have to wear what is expected of them, instead of showing up in jeans, which is harder to exercise in.
Governments make children wear GYM clothes for a reason. Have you ever been to the GYM in jeans? No body does that! It's socially unacceptable and impractical. Proper GYM kit ensures children do bring clothes specifically for GYM sessions, meaning they will have a spare pair of trainers, shorts and a t-shirt. This is a hygienic approach as many children will just use their school shoes or their school polo shirt for the workout If nothing else this is a lesson on hygiene and how to approach such situations in the real world, like going to a public GYM. Don't show up to public GYMs wearing jeans.
This limits there creativity and how comfortable they are while they are working out. Why would you do that?