Being me, I decided to make one. I didn't really know what kind of hat I was going to make, so I googled "baby boy sun hat," and decided to do something like this one. I had some fabric that my mother had sent me back when I was still pregnant. It is cotton with a background that is intended to look like denim and a cute bear printed on it. I thought to cotton would be good because it is generally rather cool. My hat is it not tested for sun protection like the one in the picture. I decided I was okay with that. He hasn't gotten burned yet.
Above are all my materials, minus a few sheets of scratch paper. I used the embroidery floss to measure David's head because I had misplaced my tape measure for the moment.
I began by measuring David's head around the widest part. I then used the good old C=2πr to calculate the radius of that part of David's head. I added 5/8 inch seam allowance to that radius and used a compass to draw a circle. If you don't have a compass, use the whole string method. I then drew a rectangle that was as wide as I wanted the hat tall plus 2 seam allowances of 5/8 of an inch and half the circumference I measured plus a 5/8 inch seam allowance long. Finally, I drew a half circle that was 5/8 inch wider than as wide as I wanted the brim of the hat to be and then drew another smaller circle inside that that was the radius of David's head minus 5/8 of an inch.
I cut all the pieces I drew out as you see in the picture at the left. The full circle should just be cut out as is, but the other two should be cut along a fold in the fabric. For my first hat, I cut two of the brim piece (the C shaped piece) but only one of the other two. If I did it again, I would probably line the whole hat and therefore cut out all the pieces twice. If you were to line the whole thing, you could easily make the hat reversible by cutting one of each piece out of one fabric and one of each out of another.
The first thing I did was sew the edges of the rectangle together so that I had a ring of fabric that fit around David's head. If I were doing this so that it was reversible, I would do so with both rectangles separately.
Then, I turned my machine to the longest stitch length and sewed around the outside of my circle, the top of the hat. Again, if I was making a reversible hat, I would do this to both circles separately. Pull on one thread to gather the edge slightly. This makes it much easier to sew the next step.
Next, pin the circle and rectangle right sides together so that it makes a cylinder with one open end. You can continue pull on the thread to help the circle fit properly. When you get it all pinned, make sure you have turned your stitch length back to a reasonable stitch (I always forget this) and sew the two pieces together. Repeat with your other rectangle and circle.
Then, pin the inside of your ring (brim) to the open end of the cylinder and sew. Repeat for the other brim on the other cylinder. You should now basically have two hats. To make them lie better, clip little vs into the curved seams.
Turn both wrong side out and pin the brims together, right sides together. Sew around the outside most of the way, leaving a few inches to turn the hat right side out. I tend to try to make this space as small as possible in everything I do because I would rather spend the time stuffing it through a small hole than sewing up the hole. In this case, however, you won't be hand sewing the hole, which makes it less time consuming.
Once you have turned the hat right side out, turn the raw edges of the hole inside and pin them. Then just put the brim of the hat under the sewing matching and top stitch around the whole brim. This will close the hole as well as keep the brim flatter and a bit stiffer.
If you want to, you could probably make the brim stiffer by stitching around it multiple times at about 1/4 inch intervals until the center of the hat, much like in the inspiration photo. Also, you could line the inside of the brim with stiff lining. I just went with a floppy brim, even though it does look a bit like a ruffle and he is a boy. He has some (blue) socks with bows too. He will live.
I am making a camo one next, mostly because I have camo fabric that was left over from when my brothers were little. I have already cut it out and it will be lined/ reversible (but it is just 2 different camos; I'm using up scraps). If you are making one for a girl, the possibilities are endless: sew ribbon just above the brim, add a flower, put lace on the edge of the brim... I don't know, play around and see what you like.