Sometimes it feels like they have a lot of homework, but that should not be the norm, because they are supposed to be taught in school with some homework for practice or get up to speed.
I would say check to see the depth of the homework, if it is minor practice on what they learned in school, then that is ok, but if it is extensive work that should be done or covered in school and it is the norm, then you need to speak to the teacher about it and get them to explain to you why the children have to do so much at home after school and if they can share an outline of what they have done in school then you can follow through to understand what has to be done at home.