This is simple but so effective. When I was 5 or 6 years old, my mom would sometimes give me one page of simple math problems. They were all basic arithmetic, things like 12+17 or 99+99 or 8x7, etc. I did them and got on with my life. They probably didn't take more than 15-20 minutes. They didn't feel like much because they really weren't. I think any 5 year-old can do them.

I believe that whatever little "edge" that gave me in learning math in school compounded exponentially over the years. I always felt "ahead" of the standard school curriculum, and that created a virtuous feedback cycle of success, which bred confidence, which bred success, and so forth.

Just a little nudge here or there at home can make a big difference.