I made this in the course of about 45 minutes from start to finish, including feeding kids and taking photos for the tutorial. I love these banners. They're bright, colorful, easy to make which is why I have no idea why they are so expensive on Etsy. I *heart* supporting handmade. I do not heart overpricing.
The hard part with the buntings (which I had no idea that was what they were called. I thought they were "banners") comes when you have different gendered kids. Trying to find a happy gender neutral colored party pennant can drive you batty. So, I made a reversable one. One side is girly, the other, not. Which means this will have to be hung where only the side you want shown shows but that's okay. Once you make one, you'll see how easy making another is and your house will have streamers all over the place for every holiday, birthday, event and day of the week. If you can sew a relatively straight line and cut a mostly straight line, you can make a really nice bunting.
I grabbed my two gallon ziplock bag of scraps and made a triangle template. The larger the triangles the less you need for the same size space. Mine are 6.5"w x 8.75" tall which I estimated would give about a 6"x8" finished triangle.
Cut out equal number of triangles for each side of the bunting. You can make this as short or long as you like. I found that doing a number divisible by 2 worked well so I can hang it evenly. I was able to use all scraps save for three triangles.