I was one of those kids who couldnt sit indian style. i say in an awkward "W" shape with my legs.
I still cant sit indian style with any degree of comfort. I'm soooo jealous of some of my dive buddies awesome frog kicks. Unfortunately, my legs dont swing that way. Dont get me wrong, im a decent athlete.....run throw hit....track a ball going 200 miles an hour.....all day every day. BUT I cant frog kick to save my life.
I am the same way with leg and knee flexibility. In fact, I am probably a lot worse. I really can't sit on the ground well--never could. When I got my certification as a USVBA volleyball coach years ago, they made us do what they called a minimum flexibility test, and I cold not even get in the ballpark on those tests. The hardest thing about scuba for me is getting my fins off. The next hardest things about scuba for me is getting my fins on.
I used to say the same thing you wrote about the frog kick--my legs don't work that way. Then I had some actual instruction. I have no problem at all with it now, and it is how I do 90% of my kicking. It feels totally comfortable. My legs aren't any more flexible than they were before.