How's that going? I learned on BASIC around 1990 but it was cool then because you could do things that were in-line with the fun/game state of the art.
Today what you can do in BASIC is "boring" compared to the most "basic" fun the kid can have on the iPad. Are you finding traction?
You've maybe (probably?) heard of it but Scratch (https://scratch.mit.edu) is a good "code-like" system for when kids are really young. You still have a way to go from 4 months of course, but I imagine it might be a bit easier to gain traction with something graphical (and colorful, and animated, etc.) than with what amounts to text editing.
We just started. It takes time for it to click. But we are making progress. I enjoy seeing his face light up when he writes something that works as intended.
You could check out BlockStudio [0], a programming environment without text (I created it). It might make teaching/explaining computational concepts more tractable with such a young child.
Today what you can do in BASIC is "boring" compared to the most "basic" fun the kid can have on the iPad. Are you finding traction?
Asking for my son who's currently 4 months :)