I think you can be “too” careful, when children are being over dressed just in case someone might look and think sinister thoughts I think we’ve gone too far. My daughter has never worn shorts under her skirt - her pants cover her perfectly well, I’ve worked with small children for years and tbh I’m more likely to see boys bum or penis when they’re getting changed for activities because they’ve pull their trousers and pants down together than I’m am to see a girls vulva through her pants. I think it’s a layer of worry parents don’t need.
Remember too that children are far far more likely to be abused in their home and by trusted adults than anywhere else, it’s right to be aware and to teach about stranger danger, and for children to know about safety and privacy, but shorts under skirts us an unnecessary step too far.