Coding - Wrote a Turtle Logo drawing program this weekend for little Jasmine (aged 4 years). It's 300 lines of Forth code, draws interactively on Windows, and generates 80's-style block-y graphics.
The user interface is an infinite loop processing 5 single-key instructions---forward, rotate CW, rotate CCW, change color, and go-home (for when Turtle gets lost!)---simple enough for a 4-year old to execute, but with enough complexity to create pretty things together.
Was delighted to hear her announce, "Daddy, this is more fun than my tablet, because I can make something with it!" Fun times, and the start of algorithmic thinking. She has plans already for more features... :)