[pmoriarty]

One of the best ways is to teach them the basics of Logo.

  to square
  forward 100
  right 90
  forward 100
  right 90
  forward 100
  right 90
  forward 100
  end

is a square.[1][2]

Then you can do:

  forward 100
  square
  forward 100
  square

etc...

Any child can get this. I did when I was 10 years old, with a bunch of other pre-teens.

Got it right away and absolutely loved drawing various geometrical patterns.

Of course, Logo is based on Lisp, so you can go pretty deep with it.

[1] - Draw it for them as you explain it, or just show it directly on the computer using Logo and turtle graphics.

[2] - Pardon if my program has any bugs.. I'm doing this from memory.. haven't touched Logo in decades...

[siraben]

That code looks exactly like the LOGO-like language aimed towards children. I wrote during a hackathon[0]. But for compactness I forgo the newlines, so the language looks like this:

  △ n = [ ↻ 30, ↑ n, ↻ 120, ↑ n, ↻ 120, ↑ n, right ]

When programming routines in Haskell:

  square :: Float -> Turtle ()
  square n = do
    penDown
    moveForward n
    rotateTurtle 90
    moveForward n
    rotateTurtle 90
    moveForward n
    rotateTurtle 90
    moveForward n
    rotateTurtle 90
    penUp

Recursion is forbidden and all loops are bounded.

[0] https://github.com/siraben/vpl/blob/4b5d39cbf8d16a988218e62f...