One of my Christmas presents this year was a bonnet for my sister in law's daughter. It was a simple (and I think awesome) gift. I used another bonnet I already had as the pattern (although I may create a pdf pattern and tutorial, because I really like them). You can see from the above picture the shape of the bonnet. I cut out two pieces of material, and overlocked them together, with the straps sandwiched between them. Leave a gap and turn the bonnet right side out, and then topstitch around it.
Place buttons on the bottom corners (the bottom part of the wonky t shape), and button holes on the curved edge. Then simply button the sides together, and bonnet!
Modelled by the accommodating Kiki. The one I made fits about 3-6 mo up.