Yes, it's a simple pose, but it took me two months to feel comfrotable with this pose. For the first month, I had to modify it by keeping my knees together, or I would be in pain. The vedio below is pretty good, but it is Youtube. Also, it does not tell you "the trick," that is, to keep your knees together if you are in pain. Eventually, you can spread your knees as wide as you are comfortable with. Also, breath and clear your mind.

http://yogawithadriene.com/extended-childs-pose/