Re: 2 players on the same xbox360 console, is this possible?
Correct. They didnt include A split Screen option for the Xbox 360 Version, only the Xbox One version.
Have you thought about upgrading? It would be cheaper and Easier just to buy the X1 as you only need 1 copy of the game and 1 Xbox live subscription.
EDIT:
So to clarify, You can NOT play Split Screen with your son on the Xbox 360.
If you want to play Garden Warfare on the Same TV, you will need the Xbox ONE version of the game. Then you can play "split screen" and you only need the 1 Xbox live gold account. Unlke the Xbox 360, The xbox one lets you only pay for 1 Gold account and then you can share that with your family.