Here are some proven Halloween costume ideas that we have enjoyed over the past few years. 

Corn baby with parents as corn holders and dog as butter
If you have a good Corn Baby Costume as a base, this costume idea is easy.  The corn holder costume for the parents consists of a green robe and prongs made from wire-reinforced aluminum foil attached to a head band.  The dog as a stick of butter  is super cute.  Get a rectangular box, cut out holes for the head and tail, spray paint it yellow, and add your favorate brand name.  Enjoy!

Hot dog in a bun with family as condiments
Cut out foam shaped buns and drape over your dog or baby with string.  For the condiment outfits, you can use small lamp shade hats covered with colored felt or other fabric to look like those plastic cone topped ketchup or mustard dispensers.  Here is a link to some costumes on eBay: Hot dog ketchup costumes

Rock Lobster
Dress your sweet baby in a lobster baby costume and have others dress in gray blob-like costumes (as rocks) or wear "Kiss" makeup, long hair wigs, and a guitar to look like rock stars. 

An unproven idea:  Lego Family
Use big boxes with arm holes and open backs.  Attach round paper cylinders (like oatmeal containers or a baby formula can) to make front of box look like a lego block.  Paint different bright colors.  For family photos, you can line up like you are all attached together.