No matter what materials you choose, it is most important that you supervise your child constantly so that mistakes get caught rather than practiced. I learned this particular lesson the hard way. When my daughter was young, she did something that needed "attention." I no longer remember what it was that she did, but I told her to write the sentence "I will not disobey my parents again" 50 times. I should have known better, but I didn't check on her at the beginning and then I got busy. So, sometime later, she brought me 50 sentences of "I will not disobey my parents agen." She had just practiced misspelling "again" as "agen" __ 50 times! I'm not certain that we ever really got that fixed. This issue of NOT practicing mistakes is extremely important. Parents shouldn't give worksheets as busy work and teachers should only use them if you are going to have a non_math teacher substitute. White boards with supervision are always a better way to practice skills. If you need some time to do chores, your child will get much more benefit by helping you with the chores. And maybe you can work in a little discussion of numbers or counting while you do chores together.
People have to start from the ground, then first step, second, third and so on to reach their destination floor. Exactly the same way students have to start from Kindergarten, then grade one, grade two and three and so on to reach their math destination. Also, if some of the steps are broken in the staircase, it is still hard to reach the desired floor using those steps. Same way, if you are missing some of the basic concepts from elementary grades, math for you is still hard. Now, the kindergarten, first grade and second grade are like first couple of the steps of the stairs. You can learn this level of math easily, as you can jump enough to take yourself to second or third step of the stairs easily. As it is very hard to reach sixth or seventh step of a stairs by jumping from the ground, exactly the same way to learn grade five or higher grade math is very hard (or impossible) without having the good knowledge of the kindergarten to grade three or grade four math. Now, consider one person is jumping on the ground to reach the third floor of a building. Can this person make it? Never, if he is not Spiderman. For this person, to reach the third floor by jumping is impossible or very hard and finally he gave up saying that it was very hard to reach third floor.