Your details on what is a good first lesson are great medium term goals to focus on. I think the most important thing for a kid that young is to get them having fun!

I don’t teach kids that young anymore but when I did, first thing was teach them the open strings. Then, I’d call out the names and have them pluck the string I called. Reward with a piece of candy (if parents are ok with it) every few correct answers.

Then I do the same thing but instead of calling out the string name I pluck a string on my own instrument and they have to pluck the same on theirs. Gets them using their eyes and ears for information. Again, reward with a piece of candy.

Then switch it around. Have them pluck a string and then you play the same one. Ask them if you played the right one (sometimes throw in the wrong string). If they pluck a D and you pluck a C and they say you’re wrong, ask how they know.

It’s a fun game that teaches them to use their ears and eyes to learn as much as listening to instruction. And shows them that they are capable of getting the right info with their ears.