Lots of great advice here.
The only thing I could add is - roll with different folks and various skills. For a long time you’ll be learning from everyone and eventually you’ll have things to share.
It’ll be a blast, and also if there are folks you roll with and figure out they do some undesirable stuff (a few ones exist in every gym but it’s usually stamped out) - don’t be afraid to pass on rolling with someone.
Rely on the Instructors for guidance over students.
You’re not new to learning or people thinking about it. I’d just say for skill development - variety of folks and body types. I rolled with higher belts exclusively for a few months and it did push me and my defense sharpened a lot from what it was. But! My offense didn’t, because I couldn’t experiment with them because they knew what I was going for. Other white belts won’t know that as readily.
Eventually you’ll get higher belts with those things eventually too, but just something to keep in mind.
ETA:
I forgot to add - that’s how I would work out new submissions. Practice with the white belts and partner with them during training too it pushed me to be on top of explaining things and I also could experiment different theories with. That was after 9-12 months though. For that first 9 months it was “Survive against this Purple belt for 30 seconds” - don’t tell him that, but it was a way to push myself when facing a clearly more advanced person in Jiu Jitsu. Or “Don’t get arm barred by (insert name)” - there was one guy who was just arm triangling everybody. I specifically would go in those rolls and know ahead of time - that’s probably what was coming. So, just try to prevent *that*. I think these little tweaks, “wins”, and adjustments help someone stay positive in a sport with a very high attrition rate. Have fun! I hope it’s a good bonding experience with you and your son! I’m jealous and hope to do that some day!