While on the road,lately I have been seeing alot of people(mainly kids) in the passenger seat with thier legs ontop the dash over the airbag.So I was wondering that if they were to get into a accident and the airbags deploy would the airbags fling thier legs and shatter thier hip bone?

My mom keeps talking about this only she says that if i cross my legs in the passenger seat (with one foot on the floor and the other on top of it pointing toward the driver)that if we got into an accident the airbag would break my leg. Is this true? i would love to prove my mom wrong.