He is adorable. I did not know if you got my previous message but if you want to measure his head circumference I can custom make a hat and sell it to you from my website. www.terriscustomcrochet.com or list it on here and hope you win :-)
It will fit 12" to 14" Head Circumference. I doubt it would fit your 5 month old. I do sell custom made teddy bear hats on my website. www.terriscustomcrochet.com if you would like to buy one. Otherwise let me know the size you need and when I get a chance I can list it on here.