It depends on what you have kids doing for homework.  America is now full of lazy, ignorant people.  They don't do sports, they watch sports.  They don't do math, they punch a picture button on the cash register.  They don't know science, they just eat organic and food without glutten because some Hollywood actress says it's the only safe food.

The kids in sports have the highest grade point average in schools.  The kids taking math and science classes are the ones graduating into jobs.  Jobs that pay 80k to 100k  starting wages.  The rest live in basements.

You can't develop the skills or attitude necessary for success in the modern world if you don't start when kids are little.  They have to know that their future belongs to them and they are responsible for creating one.  Too many kids today have too much free time spent on video games and just "hanging out." 

Part of the problem is the curriculum of the schools with their feel good about yourself programs, baby sitting attitudes and sex ed at the kindergarten level.  But a significant portion of the problem rests with parents who don't demand that their kids do school work, don't take them to museums, art galleries or vacations that give the kids a view of America rather than a view of a plastic mouse.

Down time and unorganized play that requires imagination is important but you do have weekends and summers.  Don't waste them.