The saftey considerations are solely up to the OP, but I agree with those that said everyone's comfort is likely to be improved is he/she buys a seat for the 14 month old. Mrs. dchristiva and I flew from PHX to JFK with our 6 month old a month or so ago, and that 5 hour trip was pretty long with him as a lap infant. We got the last two seats on the plane, so buying him his own seat wasn't an option. We all survived, but I don't think I'd try it again.