Natto is indeeed disgusting on first experience, but my 2-year-old eats natto and rice for breakfast every morning (this is in Japan). We've tried to vary it up, but he insistently shouts natto!
I first experienced it at age 15 and it was revolting -- stinky slime with small soybeans in it. BUT I ate it to be polite to my Japanese hosts... and lo and behold after about 5 times I found myself wanting more. Now I eat it regularly, and find it delicious. :)