M.G.
If you search on here, there's not a lot, but one mom mentions having one lanced at an ER (I didn't know what one was so searched).
You don't mention swelling though. I'm guessing it would be a bump?
Hopefully the specialist will be able to remove it for him - I think you're smart to get it looked at before it gets any bigger. These cysts tend to grow from what I've seen on that show (Dr. Pimple Popper).
Search Pilonidal Cyst and Tailbone Cyst or lump in the search bar on here and you might find more results from moms. Good luck :)
ETA - I hear you (saw your SWH). We would go the route you are too. I actually had never heard of them. Glad it hasn't swelled yet and he's not in pain. Hope someone here can share their experience with you.