Cooper or Chubbs?

Cooper is getting older, talking more and getting much better at bugging his sister.  He loves her and always wants to be doing whatever she is doing.  Ellie has a new game with him now.  They start by pretending they are both doggies crawling around the house.  Then it changes to Cooper is the dog and will go fetch a ball Ellie rolls down the hall.  Ellie has told us, his dog name is Chubbs.