Scratch is the block-based coding language made by the Lifelong Kindergarten group at the MIT Media Lab. You build a program by dragging blocks together instead of typing, so nothing is ever misspelt and nothing crashes β which leaves a child free to think about the idea rather than the punctuation.
Scratch is completely free, and always has been. There is nothing to buy, no subscription, and no paid version with more features. Anyone telling you otherwise is selling something MIT gives away.
At this age the goal is cause and effect: I put a block here, and the cat did that. Nothing needs to be finished or neat.
Use ScratchJr on a tablet at this age. The ideas below are the same; the blocks just have pictures instead of words.
The cat crosses the screen when you tap the green flag.
Build it β Project 23 blocksClick the cat and it greets you.
Build it β Project 35 blocksTwo characters have a short conversation, taking turns.
Build it βStar Blocks, this site's own language, runs inside the page with nothing to download β and teaches the same ideas.