Nike or adidas jogger pants with the stripe down the side and the zip at the bottom.
Uniqlo joggers.
Slightly nicer tee shift, plain color or possibly a graphic if it’s something he’s into or possibly from someplace he went on vacation. (My son likes the graphic tees at Uniqlo many of which have an anime vibe).
Some kids will occasionally wear polos or a button down like a Hawaiian shirt but this is rare, at least in public school.
A couple hoodies. If you want to be fancy get a fancy brand hoodie like vuori or lulu, but most boys will wear American eagle, gap, Nike, champion, U.a, etc. avoid the ones with big logo names across the front.
If he likes pink, I think he could wear a pink tee shirt with black adidas track pants and be fine. Like this one:
https://www.uniqlo.com/us/en/products/E455365-000/01?colorDisplayCode=12&sizeDisplayCode=004&gad_source=1