Math: If you want to help them with numbers and math, things such as online bingo and online snakes and ladders can help them. They learn to identify numbers as well as basic addition and subtraction. This can really help them. Games are a great way to teach. Words games help them with the alphabet and how to spell.
Spelling is something which is critical to a child's education and their literacy. At an early age, you want them to be on their way to reading and writing. Books play a big part in this. You have to read to them and instil in them a real love for literature. A kid who doesn't like books when they are 4-5 isn't likely to be any more enthusiastic for books when they are 15-16. This is just the way that things work.
If you want to assist them with their co-ordination and things of a physical nature than there a number of things you can do to help them. After all, Tiger Woods was already swinging a gold club by age 3. Throwing balls to them and getting them to throw and catch will help them with their hand-eye co-ordination. If you want them to play soccer, get them to start kicking with both feet. Giving them a grasp of the fundamentals at such a young age with aid them immeasurably. The common element with most successes is that they started at a young age. Swimmers, gymnasts and tennis players were already doing what they were doing by a very age. If you don't start something by the age of 15 it might not be too late but it's going to be a struggle. You don't know if online bingo or classical music does anything, but it's better than nothing.