HOW TO SET UP TWO NINTENDO SWITCH CONSILES? DS (13yrs) BUYING HIS OWN

[sweetpea6002]

I have three kids (13, 11 and 8). They have a Switch between them with a mix of cartridge and digital games. Now my eldest son has saved up enough money to buy his own Switch Oled. He’s been saving for ages, really wants it.
My question is - once he buys it, how do we set up the second console? I want to put parental controls on it (to limit the time he spends on it and to stay off age inappropriate games). Apparently I can link the second to my main Nintendo account, one becomes primary and the other, secondary. But the secondary console would only be able to play downloaded games whilst online (whereas the primary console can play downloaded games offline). OR do we just take the carrridges with us on journeys to avoid arguments?

Has anyone else done this who can advise?

thanks v much -haven’t had the current Switch for very long so still finding my way with this.