No I wouldn't do it. Its not just emergencys but if you talk to air hostesses they can tell you a host of stories about normal kids being upset and scared. At 5 my kids couldn't do it. Some maybe not mine. 10yr old on a 4 hour flight ok.
Why is domestic different? Fly to nz takes 3-4hours.
Its sucks it costs so much even when you book way in advance.