Miyake in Portland - bad idea to go with 3 1/2 year old?
I hate to say it, but its really not appropriate for a typical 3 1/2 year old. The place is very small (the bathroom is in the kitchen!) and the menu is small and quite specific - a "side of tofu" may not even be an option.
Yosaku is kid-friendly but is an entirely different thing. If you want to experience Miyake I would try and find a sitter.
I agree with other posters. Miyake is incredibly good, but not for young children. The space is tiny and tight, the menu is very creative, and there may not be anything on it that your child will like. But, don't deprive yourself of the pleasure of eating there, it really is outstanding.
Yosaku is very good for kids. Our daughter loved their children's bento box. I think you would be very comfortable there with a child. And, although it is very different than Miyake's, you'll have a good meal as well.