The Moen Posi-Temp shower fixture takes the 1222B cartridge.
Moen replacement 1222 for the Posi-Temp Shower Valve
Seems my son snapped off the connector to the unit. So, need a new cartridge and internal parts? Could someone tell me what brand this unit is please
UNfortunately, the piece you need in order to "easily" remove it, is what broke off. I am not sure how YOU are going to extract the remainder, but do NOT do anything that will damage the brass body or you will be replacing the entire valve. I have some speciallized tools to solve a situation like that, but you do not and it would be cheaper to hire a "good" plumber than buy them. At least your cartridge is intact. The last one I had to remove the customer had already destroyed it before calling me which made it even more difficult than normal.
Licensed residential and commercial plumber
A 2x4, 2 3" wood screws.
Put the wood screws through the 2x4 as close to the center of the cart as you can get in the north and south position in the meaty part of the plastic. Use leverage and pull 2x4 and cart straight out. You might have to twist the cart left and right to break the hard water build up before you pull.
FYI, we use this as a last option resort when the home owner has screwed up the valve like this. If you are unsure, call a professional.
Be careful when using the "pull hard" approach. I have seen the valve come loose in the wall, which for one unlucky fellow resulted in the backer-board and tile being damaged when it let loose.