I suspect you already have thought of this, but even if your child won't receive "grade book" credit for doing missed work, s/he should still do it, and still turn it in. Attach a note saying that you understand that credit won't be awarded, but if it isn't too much trouble it would be great if the teacher could give informal feedback about how well the assignment was completed. That way, your son/daughter has the opportunity to practice the skills other students have worked on. The teacher may not go so far as to fully grade it---it's much easier to grade all copies of a certain assignment at once than to do them slowly over time---but you should still get back something.
There is a secondary benefit to this---even though grades are supposed to be objective, they never are. Students who are 'serious' often get the benefit of the doubt.
This is one reason why, when I give exams, students are to write their SIDs on the answer pages, and not their names. Since we only administer a midterm and a final, my teaching assistants aren't able to tie answers to students, removing biases they may hold when grading answers.
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