Honestly it is a little creepy but if he sees it, he sees it. Maybe frum women who care about such things should be more careful when they sit in such places. But perhaps this is on him as well - if his work environment means he has to crawl around on the floor and his visual perspective is form that angle, maybe he needs to make adjustments. I am not sure how he expects women to protect the view from below. Maybe he should have a raised seat of some sort on a platform or whatnot and have the kids try ont he shoes so he can continue standing or sitting in a regular chair rather than sitting on the floor and looking up from below. If he found a creative solution, he wouldnt be looking up women's skirts.