The storyline where Roscoe Plunkett wants live full-time with his dad Baxter and stepmother came about because the actor playing Roscoe (Blake Garrett Rosenthal) no longer wanted to be a series regular, so they created a reason he would still be in the series' continuity with much less screen time. Rosenthal actually stopped portraying Roscoe early in MOM's 4th season and retired from acting after that.
Allison Janney (Bonnie) & Octavia Spencer (Regina) also worked together on The Help (2011) as Charlotte Phelan & Minny Jackson respectively.