7 yrs old nephew is obsessed looking up my skirt

I'm in my early 40's and very fit. I wear dresses/ skirts everyday for work and am very professional. No cleavage or see through tops. However, I do wear very short skirts. They tend to be loose pleated skirts/ dresses a few inches below my pantyline. I've always dressed this way.

Ok. So, my nephew is 7 yrs old and a very sweet boy. He's always been affectionate and loves being around me. I babysit him often. A few months ago, I was in the kitchen fixing myself a drink and caught him looking up my skirt. He must have been there for quite a while and I didn't notice, since I was on the phone as well. I apprehended him and told my sister. Everything went fine. Now he seems to be positioning himself so he can see up my dresses. Like laying on the floor and putting his toys there. I think it's on purpose. He's like my shadow now and always behind me. I know that he's looking right up my skirt every time. It's quite frequent now. Any suggestions on how to handle or is it just a boy thing that he'll completely outgrow?