I tried abc mouse with my ds and didn’t like it at all. It was a lot of puzzles and coloring and I didn’t feel like my ds was learning much. We use Reading Eggs/Math Seeds instead. My ds is 3.5 and already knows 80 sight words and can read books by himself. It’s an amazing program and really does work to teach reading. I don’t like the math as much and they give you the choice to pay for just reading or both programs. My ds likes the math more though, probably because there are a lot more silly videos and songs.
We started him around that same age. It teaches letters and sounds first then moves on to sight words. They have a program called Reading Eggs junior to start them on and then they can move to reading eggs when they’re ready.