Help with new ZTE Allstar, invaded by sons phone

[AC Question]

I just bought a new ZTE allstar, as soon as it activated, all of my sons contacts showed up on it, I deleted them, and added my own. A notification popped up on mine saying I couldn't delete that many contacts at one time and did I want to add them all back in, or wait to decide what to do, I chose wait. now my son tells me all of his contacts are missing from his phone. Now I cant find the notification on my phone to get his contacts back. Also my son is all over my new phone, google play store, gmail, how do I get him out of my phone so that I can open my apps?
We both use Straight talk, I'm not sure what his phone is.