W-sitting refers to sitting on your bottom with legs out to the sides, like the shape of the letter ‘W’. This position, although it offers more stability, puts pressure on growing joints and muscles.
You may find that your child uses w-sitting occasionally when transitioning from crawling to sitting, but don’t let it become a habit. Offer a variety of options such as, “Lets move your legs in a V shape.” “Criss-cross, applesauce.” “Can you side sit like this?” “See how Mommy has her legs straight out in front of her?” All of these are more beneficial positions that engage and strengthen the core muscles.
Here are more articles to read up on the subject.
http://www.physioquestions.
http://www.pediatricservices.
http://nspt4kids.com/