I have never tried this, but I do know that children thrive on the attention that what they're doing is important. Especially if what they're doing requires hard work. If and when you do find the right environment (one doesn't automatically come to mind if the Python or Racket interpreters aren't good enough for you), giving your children little puzzles that you think up and solve yourself -- so they can come to you for constant hints or suggestive half-examples -- is important. Your constant interest in their hard efforts will go a long way.