For anyone travelling on JetBlue with kids, I got this response from my DD, age 8. We ended up flying Delta's Flysong out of Logan for our trip to Orlando and JetBlue coming home to Boston. DD(8) liked the snack offerings on Flysong. They had a kids snack pack which included gummy bears, goldfish, applesauce for $5. She didn't like the head phones that they supplied (they were the ones that are supposed to fit inside your ears, not very comfortable). She did like their flight tracking channel and they also offered a variety of music including Disney songs.
For JetBlue, she thought their over the ear style of headphones was much more comfortable. Didn't enjoy the flight tracking channel that they offered and they didn't have music, but they do have Nickelodeon (big plus in her book). JetBlue does have a selection of free snacks to choose from (small package of pretzels, etc.), but nothing for sale.