"I think he's going to make the world's best [grandfather] because he is so animated," McCarthy, 37, told PEOPLE at ABC Family's World Record Elf Party on Monday in New York City. "I also think I am going to rock as the grandma. I love her and I am excited about this baby."
Although McCarthy admits that she can be pushy at times, the former playmate says that she and Carrey, 47, are going to keep their opinions about raising the baby to themselves.
"My biggest lesson in it will probably be to just shut up and just let her raise the baby the way that she wants it," she says. "I think grandparents can kind of overstep their boundaries. I'm going to try to be there as a friend and a cool grandma."
First task as the "cool grandma" – handling the baby shower.
"I will be planning [Jane's] baby shower in January," McCarthy says. "I have to try and think of those baby games. My mom did the chocolate Raisinets in the diaper but I'm not sure I can go there!"