Over the years I've tried quite a few pieces of software designed to help children with maths, but they all failed in one way or another. Some covered such a limited range of number work that they were an expensive luxury. Some had put far more effort into the impressive graphics than they had into making sure the maths was correctly targeted. And some offered impressive games where it was far more fun to get the wrong answer than the right one. A case in point was a game where the correct answer allowed the knight to dance with his lady while the wrong one made him drop dramatically through a trap door. I'm sure you don't need three guesses to work out which boys preferred.
Then I discovered Numbershark - the best piece of maths software I've ever seen. With 45 games and a huge range of levels, it covers all the basic maths skills and can be used by all age groups from pre-school to teenage and above. (I can set it hard enough to test my mental maths skills to the limit.)
The ability to set the exact difficulty level of a topic is impressive and allows for unlimited practice at that level, using several different games, before moving on to something harder. You can also set individual levels for each child who uses the software, so your youngest can be working on simple addition while your oldest uses his turn to practise division.
There's a built in reward element as each completed learning game is followed by another activity just for fun. Some games are simpler than others, and you may need to be selective which you choose for a child who prefers to guess instead of think.
Numbershark 4 is not cheapest piece of maths software on the market, but it's a good investment that should last for years and see your children right through school.