With adaptive learning, the programs won't move on to the next level until your child has a firm grasp on the current material. The online games will be a wonderful way for your child to catch up on basic arithmetic concepts and be comfortable using them across applications.
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.
This sounds like an awful lot, doesn't it! A good set of preschool worksheets should cover all of this, and more. In the preschool years, repetition is the key to learning, but you should look for worksheets that teach the same skills in a variety of ways. This not only prevents boredom setting in, but also reinforces the concepts by encouraging understanding as well. The importance of reading to your child cannot be emphasised enough, and you should encourage them to 'read' as much as possible too.
Just because your child will be playing fun online games doesn't mean the same value won't be there. Create a comfortable study zone. Turn off outside distractions such as cell phones, radios or TVs.