Feet wont point in Childs pose?

I am a yoga teacher and I have found that child’s pose can be very difficult for a lot of men including my husband who can’t point the toes and sit back on his heels in child’s pose. He has to curl the toes under. I have noticed this with lots of men in my class. So my question is this due to really shortened over worked shin muscles or is it purely an anatomical structural thing that will limit him ever being able to do this? Any suggestions, advice to free my husbands feet? Haha!