none of the cartoons you describe "road runner, bugs bunny and crew, daffy duck, foghorn leghorn, jetsons, flintstones, pepe le pew" were designed for children. the loony tunes/merrie melodies cartoons (bugs bunny and crew) were created for theatrical distribution and the jetsons and flintstones were sitcoms intended for primetime broadcast.
if you're thinking of cartoons with smartly written scripts and were written for children perhaps you should have mentioned "rocky and bullwinkle". sure the animation was cheap, but that's the limitation of teevee budgets.
you're right about the corporate churn, though. hardly any saturday morning cartoons went for more than a half season or so. just not enough time for a series to find a voice or for the writers to get a feel for making it good.