Create some easy bunting with ripstop fabric. Ripstop fabric is the stuff that kites and parachutes are made out of. It is easy to sew and doesn't fray so you don't need to edge the bunting triangles. It's also water resistant so this bunting would be great for an outdoor setting.
Different colours of ripstop fabric
Ribbon (the length you want the bunting to be)
Sewing machine or hot glue gun
Cut out triangles of different colours of ripstop fabric. You could cut a cardboard triangle first to use as a template. Cut out as many as you need to go along the length of your bunting.
Pin the triangles along the ribbon.
Pin the triangles along the ribbon
Sew the ripstop triangles onto the ribbon with a sewing machine. I find a zigzag stitch easiest as the fabric doesn't bunch up or slip. Remove the pins as you go. If you don't have a sewing machine you could try a hot glue gun.
Zigzag stitch on the machine
Your bunting is now ready to hang.
If the bunting is to decorate a child's bedroom or playroom, you could try making some coordinating ripstop hot air balloons to go with your bunting.
I buy my ripstop fabric online from Fabrics'n'Stuff. They sell cheap remnants and can post internationally.