I got it! Cookie would be perfectly played by Shirley Temple! They're both round, playful and incredibley cute. And Peaches can be played by Bonnie Franklin, the mom in the old sitcom "One Day at a Time". They both are tough and no-nonsense when they have to be, but still good loving single moms to their kids. So, here's my cast:

Peaches.......Bonnie Franklin
Big Mac.......Chris Farley
Cookie........Shirley Temple
Pepper........Whoopi Goldberg