Take the ladder off of the bunk bed. This makes building the fort easier.
Measure the distance across the front of the bunk bed. Cut a strip of the auto adhesive as long as that measurement.
Pull the adhesive apart. Pull the paper off the sticky part of one of the halves of adhesive strip. Stick the strip across the bunk bed between the bottom of the top bunk and the top of the bottom bunk.
Measure the distance from the floor to the strip of adhesive. Cut an old sheet to fit perfectly over the bottom bunk.
Stick the other half of the auto adhesive to the top of the sheet. Attach both halves of the adhesive together, allowing the sheet to hang down over the bed.
Find the center of the sheet. Cut a flap in the center to use for a door.
Cut up different colors of felt fabric and glue them together to make a flag for the fort. Allow the flag to dry before handling it.
Attach a yardstick to one of the top corners of the bunk bed using a zip-tie. This is the fort's flagpole. Glue the flag to the top of the flagpole.
Place the ladder back on the bunk bed over the top of the sheet. Fill the inside of the fort with pillows, blankets and soft toys to make it cozy for the kids.