I liked wearing shorts under my skirt in primary- I did on PE days, but not in the rest of the week. I can remember, towards the end of primary when I was self-conscious, wanting to practice cartwheels at break but as I didn't have shorts on that day, feeling too shy to do so. (It never occurred to me to just wear shorts every day!)
But making them compulsory is really backwards. It will point out to the girls that their bodies are something to be ashamed of and hidden.
The Times article says "Retailers including Next and River Island market trunk-style underwear or cycling shorts as “modesty shorts”, while Gap calls them “cartwheel shorts to layer under dresses”. Next sells its “modesty shorts” for girls as young as two, while River Island sells them for those aged five and over."
I like the term "cartwheel shorts" better than "modesty" (which is gross), but they turn out to be made of polyester. Tight polyester shorts, all day every schoolday, does not seem healthy. I had a search and M&S do cotton jersey kids' cycle shorts (in the PE kit section; no weird modesty labelling) which do at least come in white, which would probably work best under summer dresses.
I agree that having proper shorts as part of the uniform, and normalising girls wearing them, would be much better than forcing them to wear an extra layer.
Shouldn't primary-aged kids normally have an adult out supervising them in the playground anyway, which should stop perverts hanging around or taking pictures or generally being inappropriate?