If it ever comes down to Cassidy being placed in the custody of Meredith or Linda F., what sort of trauma will that do to Cassie, as far as transitioning from one familiar lifestyle to another. I believe that the Youngs (Jason, Mamma, sisters, etc.) wanted to keep Cassidy away from Michelle's family for several reasons: to keep Cassidy from remembering them. She was so young. It's easier to forget. Next, of course to keep Cassidy from being questioned by anyone or for keeping anyone from hearing Cassidy say anything that would be "telling".
Certainly there is trauma from Cassidy's seeing her mom dead in the room. There will be post traumatic problems affecting her as time goes on and she learns more. There is psychological trauma when moving a child Cassie's age (at the time of Michelle's murder) from one lifestyle to another (her mother's arms and care into Mamma Young's lair).
Then, if Cassidy is put into the custody of Mamma Y. or Jason's sister or the Fisher family, there will be yet another trauma to Cassidy. All the way around, this child (as with the Cooper children too) are forever traumatized now and down the road.
I suppose I am only thinking out loud here. Stupid stupid adults who kill. They kill the child in the long run.