does my son have to go to Canada to renew TD

Hi,
I am about to apply for a 2nd TN visa at the end of February. My current TNexpires in early March. I have a 17 YO son living with me in the US on a TD visa. When I go back to Canada to apply again, can he stay in the US?
How would I renew his TD, can I do both with his passport and birth certificate?

Thanks

He needs to either go to border or file I-539 by mail after you get your new TN. You cannot get the TD for him at border.