No. You do not need to buy the games again I recently switched from the quest 1 to the Quest 2 and you just have to go pair new headset in the settings page on the Oculus app and then login with the email or Facebook account that you used on your old one with the other handset and once you finally get onto the Quest 2 or any headset we are games should be there for you to download for free again.
To get full access on the second Quest 2, you'd need to reset it and set it up with your son's account. If both are set to the same account, you share all games (but multiplayer can be tricky, many don't like more than one person on an account in the one game at a time).
Or there's the new app sharing thing, where your son would need to add your account as a sharing user, then you'll get access to most stuff (games were able to opt out of sharing). I've never tried it though, I only have one facebook account for Oculus so can't test.
To enable it, your son needs to put on his headset and do the following: https://support.oculus.com/240510240887582/
Then probably some more steps to add you, but that's further than I've gone so far.