I don't mean to pile on and I really can sympathize with you but....

Holiday evening, JFK, 3 children (1 being an infant I'm assuming you needed a lap child ticket for), luggage to check, no way would I think 90 minutes was enough time to navigate all that.

Knowing that your luggage had to be checked 60 minutes before flight time, you only had 30 minutes to wait in line. Which you blew outside waiting on the SkyCap.

Having said all that, I don't think you should have been charged the change fees. I would persue it but with low expectations.