I have knit this hat quite a few times, for babies and toddlers and it is SO beautiful. I've done it to look like tomatoes, eggplants, pumpkins, etc. I use 100% cotton such as Peaches and Creme or Jo-Ann's version of kitchen cotton.
My toddler hat was done with a size 8 needle. I always use the same pattern, but bigger needles and have no problems at all. My original pattern for this hat was not at the site you shared, but here: http://acechick.typepad.com/knitchicks_patterns/2006/01/strawberry_bean.html
Maybe that will help you more. Please, let me know if you have any other questions.