Blow up balloon. Prepare papier-mâché: Mix together 2 cups flour and 3 cups water. Cut newspaper into 1"-wide strips.
Dip newspaper strips in papier-mâché mix and cover 2/3 of balloon, laying strips flat; let dry.
When dry, trim away rough edges to resemble an eggshell. Trim at narrow end to create a neckline and at wider end to make room for your baby's legs (you can cut more away later when you fit it to your carrier).
Paint shell in two colors as shown; let dry.
Buttons: Cut individual cups from egg carton, add stickers to centers, and hot-glue to shell as buttons.
Belt: Cut a buckle shape from top part of egg carton, and cut a strip of paper for belt. Weave belt through buckle and hot-glue to shell.
Punch holes in papier-mâché body in four places: on top at both sides of neckline and on bottom at both sides of waistline.
Cut and thread lengths of 1/2"-wide ribbon through holes. Tie egg to baby carrier so the baby can be taken out of carrier while egg remains attached. (Trim more from neck and leg openings, if needed.)
Collar: Fold two coffee filters in half and secure to carrier with double-stick tape (put these on after the baby is in the carrier). Repeat with additional filters.
Bow tie: Cinch an accordion-folded 6"x 6" paper square at center, wrap a small strip of paper around it, and secure with tape. Hot-glue bow tie to collar.
Use double-stick tape to attach collar to carrier after baby is placed inside.
Originally published in the October 2015 issue of Parents magazine.