Personally I think gum needs to be outlawed on planes. I just got back from WDW. On the way down there was gum stuck (hidden) in the crack of my seat and it got all over me. On the way back, DS went to open the emergency instructions, and they were stuck together. You guessed it, another disgusting gum wad. Makes me want to puke, not to mention people looking like cows with their cud while chewing it. Singapore is sounding pretty good right now. Public caning for gum chewing. If I caught the person that hid the gum in the seat crack, it would give new meaning to the words "air rage".
There are a lot of options which work just as well, sucking a hard candy or safety pop, sucking on a bottle, or Ear Planes all work just as well and don't make a filthy, disgusting mess for your fellow pax.
Especially if your kids don't chew gum at home, they are very prone to playing with it and getting it all over themselves, their surroundings, and everything else. A steel tube hurtling through the stratoshpere is NOT a place to experiment. If you're bound and determined to give it to them in flight, at least give it to them for a couple months at home first, so they learn what not to do with it by making a mess of their home before you take them into a tightly cramped public area with it.
Anne