What is 'W' sitting and how does it affect a baby's growing body?

'W' sitting, also known as frog sitting, is a position wherein toddlers and babies bend their knees and keep their feet flared out behind. Physical therapist Kathleen Finnan warned that this puts a "lot of force on soft, flexible bones and joints" of a baby. It could lead to weak core muscles, joint pain and arthritis, etc, she added.