Class 2 son races through his homework in ten minutes, mostly right. Give him more, or leave it?

He sits down after his snack, finishes everything in about ten minutes and goes off to play. A couple of careless mistakes, otherwise fine. His older brother in class 9 takes two hours over his and thinks this is very unfair. My mother thinks we should buy a workbook and give the little one a page a day so he 'gets the sitting habit'. I'm not sure a 6 year old needs more work just because he's quick. Do you add anything at this age, or leave it?