There is a charge at the moment - this will end in July also the size of the family account will change from 4 to 7 people.
My youngest three children have cards under my wife household account. They enjoy checking their miles, points and status. Interestingly under 12s get full points and miles even when on child reduction tickets ( Other OW airlines sometime give signifinance child discounts espec. if parent is on a full premier fare).