Ask HN: Toys or materials to teach 3 year olds “programming”?

Hi, I'm looking for some fun materials that would help my boys to develop interest in basic concepts of programming like procedures, types or loops. I know some of you will probably tell me it's too early and that at this age it's all about building relations and whatnot, but they already seem to be way smarter than I expected them to be so why not point them in a new direction? Anyway, any ideas are appreciated :)