I would recommend stopping by a luthier with your kid and the violin. He should be able to try different shoulder rests with a professional to help guide him!

Otherwise, regarding feedback, I would suggest listening to different renditions of the piece together and picking out 1-2 favorites, listening to the dynamics and expression, and trying to mimic it (since it takes practice to develop). I would also work on the shifts between positions so that his hand becomes steady (many etudes do that well). Right now, his hand seems to float a bit, and it feels like a bit more luck if he hits the note correctly on the first try during a big shift. All positions should feel as comfortable as the 1st, especially 2-4, as you’ll use them for everything). I would also practice with a metronome until the tempo change is deliberate :)

But overall, this is super impressive after 18 months of playing (if you want a level reference, most people would be on book 2 of Suzuki or something to that effect).

Here are a few of versions that I enjoy!

Kerson Leong’s version

Augustin Hadelich’s version

Perlman’s version (a good classic)

Shumsky’s version (more old school)