I hated school when I was 8. But I loved it whenever we traveled for a vacation. Meeting new people, seeing new things, eating new food, dropping out of my regular social circle... I enjoyed all of that the most in any given year. So, travel a lot. Museums and tourists spots of course. But also go to out of the way places. Visit new countries, if you can afford it. Maybe poorer countries as well, with significantly different lifestyles. Maybe show him religious places (I'm sure you're not religious) or take him on a pilgrimage just to see how much religion affects the rest of the world.

Take him outdoors such as hiking, camping, sailing, fishing and so on. Maybe you can learn some biology and botany and show him the vast diversity life we never come in contact with. Bird watching is also a lot of fun.