I want to get my 13 year old coding. I have a RPi3 I downloaded Retro pi so he could check it out. He went online and found all the cases that are out there for it. He wants one so he can build the retro pi game system. He will get board with the game system soon enough. My question is if we use the zero for Retro-pi and want to later add raspbian will we have enough RAM to do both or should I buy a different model to begin with?
My question is if we use the zero for Retro-pi and want to later add raspbian will we have enough RAM to do both or should I buy a different model to begin with?
RAM isn't an issue WRT to multiple operating system installs, since you can only run one at a time. What is relevant is permanent storage -- i.e., the SD card size. And the easiest, most trouble-free thing to do if you want to use different operating systems is to put them on separate cards.
However, a few things to note about the Zero:
It only has a single USB OTG port, meaning you will need a hub if you wish to connect multiple input, etc., devices. The power available through the port is probably less than other models.
It has a very odd duck "mini" (not "micro") HDMI port, for which you will need a special adapter. This adds a bit of fragility WRT snapping things off.
So it may not the best choice to use as a headed system (display and input devices attached) for a child. However, it's perfectly feasible to do what you want.