from a crash safety standpoint, most companies assume the rear passenger's height ( who could be child or adult ) is a middle ground of 57 inches tall ( almost 5 ft !) , so most oems design rear seat cushion ht, seat squab angles, seat belt anchor point/ seat belt shoulder/ neck drape location , etc to that height .

    but....you see most kids demanding to dich the " babyish " booster seat well before that ht, irrespective of the car model whose main consequence is putting the seat belt dangerously on the very soft and squishy neck, not the strong mid shoulder ....so you need one of those simple inexpensive padded triangular gizmos avail everywhere to keep the belt drape in the proper location until they are tall enough : ( generic internet pic...not my kid ! )