Your post is alarming but quite interesting. First of all, you use the pronoun "we." Who was flying? If both parents were with the child, did you have 2 aisle seats and 1 middle seat? Please clarify.

What was your reason for switching out of the window seat? (Just wondering). Then, are you saying that the Flight Attendant obligated your child to fly without a CRS (child-restraint-system) instead of allowing you to use the CRS in the middle seat, even though it seems that was your only option? Did the FA make any attempt to move you and your child to a window seat since, according to her and JetBlue's website, the CRS can only be used in a window seat? If you answered yes then no to the previous two questions, it seems you have a serious complaint on your hands.

As to your questions about JetBlue and FAA policies: First of all, a CARES harness is a CRS (child-restraint-system). Second of all, JetBlue's website does say that CARES seats are restricted to window seats because it says, "Safety seats or CRS should be placed in a window seat. It may be placed in a middle seat or aisle seat as long as the other seat(s) remain empty. Safety seats may not obstruct a customer’s pathway to the aisle. Safety seats may not be placed between two individuals." Finally, the FAA website confirms that you should, "Reserve adjoining seats. A CRS must not block the escape path in an emergency. Many airlines have policies that require a CRS to be placed in a window seat. Do not place a CRS in an exit row."

Personally, I found your post very interesting because my family and I are taking a 5-hour international flight in less than 2 weeks, and we will be trying out the CARES harness for the first time. Our return flight is on JetBlue. Thanks for this valuable information and I look forward to hearing your response!