What is the equivalent of that today? For instance, is there an easy-to-use Python library that lets kids do simple drawing with ease?

Ie, on the TRS-80's Level II BASIC, just doing SET(X,Y) coloured a white pixel at that coordinate, and RESET(X,Y) turned it black. And you could see immediately the utility of applying FOR loops to make horizontal and vertical lines, etc.

I don't remember QBASIC, but the customized BASIC on my Tandy 1000 In the late 80's had graphics modes with I think PSET(X,Y,C) to light pixel with color C, and even had some built-in commands for making line, rectangles, circles, and ellipses.

So it was very easy to type a few lines and get something cool on the screen, but still required a bit of thought on x,y coordinages and some programming constructs to do anything complex.

I only dabble a bit in Python, but what's the best way to do something like that today?

I think there's much more of a feeling of "Wow, look what I made!" after drawing something this way than just using the painting mode for sprites in Scratch.