There are many good workbooks available for kindergarten children. However with a regular workbook, a child can do each activity or worksheet only once. A good option is to use printable kindergarten worksheets. These are basically digital versions (like ebooks) of worksheets that can be bought and downloaded to your computer from the internet or from CDs and then printed out. The advantage is that you can print out whichever sheet you wish. If you need to re-inforce a certain concept more you can usually print out that sheet again. Of course you will therefore need to have a computer and a printer.
Math concepts can also be reinforced for the children throughout the day on a regular basis. Try placing an enlarged number 12 above the 12 on the clock and label it "lunch time". Label your clock with as many of these types of labels that you can. This will help the children to recognize the way the clock looks when it is on the hour. Make sure to point out the clock when it is time for lunch by saying, "Look at the clock, it is time for lunch. See the little hand is on the 12". You can also incorporate math through songs. If you are learning about monkeys, make it a point to sing, "Five Little Monkeys Jumping on the Bed". The same concept can also be used when you are reading books to preschoolers. There are plenty of books that incorporate counting into their story and will follow the theme you are teaching. Math is a concept that children will have to use for the rest of their lives and that will be continuously taught in school. By starting off their education with fun math activities, you can get them started with math the right way.
To Pay or Not to Pay? There are hundreds if not thousands of free printable worksheets available online. These are ideal for filling time or keeping the kids busy on a rainy day, but few of them offer a systematic set of worksheets with activities designed to teach your children a specific set of skills. If education is your aim, you may have to spend a little to get useful, comprehensive worksheets that actually help your child to learn.