If you do want to produce your own worksheets and don't have the Microsoft software, you can download free tools like OpenOffice or use an online word processor or spreadsheet such as the free Google Docs which help you do similar tasks. You just need to create a table with as many rows and columns as you need and then type in some numbers before printing it off for your children to practice _ depending on the level of complexity choose single digits or multiple digits. If you're not sure what level to start at, aim low, start with easy numbers and see how your child goes, the self_esteem boost they'll get from acing the first worksheet will give them confidence for more difficult math problems.
As a math tutor for 15 years, I have tutored hundreds of students from all the grade levels. I found most of the students were not comfortable with mathematics. More than 80% of them said, "the mathematics is very hard." Why do most of the students find mathematics a hard subject and try to avoid it? The answer for the above question is hidden in a simple example. I always give the example of stairs to my students, and giving the same example in this article. I compare the steps of a staircase to the concepts in mathematics. As this is very hard to reach higher floors of a building without stairs (or elevators these days), same way learn higher concepts in mathematics without learning basic concepts is very hard.