I'm also basing tutorial on my 6 month old. I'll measure my older kids and give head circumferences and hat length at the bottom for those, so you can easily make this for just about anybody.
1/4 yd polar fleece fabric (this can probably make 2-3 hats depending on size)
1. Measure your child/baby's head. My 6 month old has a head circumference of 17 inches. For the length I chose 8 inches, as I vaguely remember reading that was a good hat length for a baby. It also gives me 1.5 to 2 inches to work with to hem.
2. Cut out two rectangles that measure 1/2 the circumference by the length. So I cut two rectangles each 8.5 x 8 inches.
3. Sew up 3 sides, leaving the bottom open. I used a serger, if you don't have one, I suggest zigzag stitch to allow for a bit of stretch.
4. Hem bottom of hat.
5. Make the pom poms. This is how I make fleece pom poms. I cut 2 strips of fleece roughly 2 inches wide by whatever length you want. A good estimate is 12 inches, it will create a full pom pom, less and your pom poms might come out puny. I recommend 8 to 12 inches in length.
Cut into the strip on either side, not cutting through to the middle, all the way down the strips. Once that is done, take both ends of your strip and give it a little tug to stretch it out just a bit. Next, take your needle and thread and roll the pom pom down the middle about 3-4 turns, then pull the thread through a couple times. Continuing doing this until the entire strip is rolled up. Pull the needle through a few times until it feels secure, then tie off. Now, fluff your pom pom to hide the center. Make a second pom pom the same way.
6. After making the second pom pom, attach each one to the points on the hat. I usually run the thread up through the inside and through the pom pom about 4-5 times before I tie off.
And you're done!!