Activating 13 Pro Max phones (plans on phones not activated)

I am giving my kids new iPhone 13 Pro Max phones for Christmas. I didn’t transfer the plans (only way to do it if you want to keep it a secret!). Is there a step that needs to be done for the eSIM (do I need to get new eSIMs from the carrier or Apple)? One has an iPhone 11 and the other has a 10.