Giving students an excessive amount of homework in the early grades can turn them away from learning. It also robs young children of a chance to do other activities after doing six or more hours of academic work in the classroom. It is only when children reach sixth grade that the amount of homework that they do is directly related to how well they achieve in school. Before then, the effect of homework on achievement is almost nonexistent.
Rather than discussing with individual teachers how much homework your children should have, a better approach would be to work through the parent-teacher organization to have the school establish a homework policy. Otherwise, there may be little consistency between how much homework Ms. A and Mr. B assign in third grade. This leads to some students being overburdened by assignments while others rarely do any homework. Also, as students get older and learn different subjects taught by different teachers, it's extremely important to have a school policy that spells out which days of the week individual teachers have to make homework assignments and how much daily homework is appropriate.