JetBlue offers guarantee to seat 13-and-younger kids with their parents for no fee
"JetBlue said it has a process that identifies reservations with children and adults traveling together who don’t have prior seating assignments. For no additional fee, JetBlue said it will ensure a traveling child is assigned a seat next to at least one accompanying adult – when seats are available."
https://www.cnn.com/travel/jetblue-g...ing/index.html