How old is your son? And with which skills do you face troubles? If he's really small, maybe it's better to wait for some time with learning, children are different and they develop with various speed and that's ok. Besides in case of reading their time for learning is between 3 and 7 years so anyway you'll have enough time for this
I agree with previous response, there's nothing bad in using gadgets from small age because nowadays technology became a very important part of our life and having for example skills of using computer is necessary for children too. But all these things should be always controlled by parents, if a child spends all time with a tablet, it's a very bad sign for his general development. Internet safety is very important too, however I don't think that it'll be necessary at least till 7-8 years.
And yeah, there are many special teaching games now for developing almost all necessary skills. For what specific subject do you need them?
If it's math, I can recommend Daisy Petals, Puzzle Hex and 12 Many. If it's reading and learning alphabet, than such games as Alphabet Space Photoshoot, CuzCuz Fire, Floyd Breakdance and Zebrainy ABC Wonderlands zebrainy.com/ .
There are really so many of them, just try to search through net for a specific type