We could have afforded to fly long haul when the children were young, but we collectively thought it would be unfair on other passengers, as we didn't know how they would behave, how they would tolerate it. So we chose to holiday in the U.K. which has proved to be amazing.
Before DS & DD arrived we experienced a flight with a baby crying continuously, trust me after 4 hours of none stop crying, we were questioning whether we were fit to be potential parents. Made worse by the fact we'd paid for seats advertised as adults only.
I think parents owe it to fellow passengers to be considerate. In my opinion the Mother shouldn't have taken up 2 seats sleeping. This obviously meant toddler constrained to Grandmothers lap, kicking the seats and so on. You plan entertainment in advance, if you're going to fly long haul with a young child.
Obviously there's a poster with excuses why a baby/toddler would 'have' to fly long haul.
I'm glad I never wish to fly again, as some people's attitudes, that they're hard done by because they're the parent, taking said small child transatlantic. How is it my problem that your child can't behave? How is it my problem that I'm being disturbed by your child.
I'm sure I've read of parents making concessions by creating comfort packs, for the seats in front and behind, with a little note apologising for any inconvenience that might be caused. That's the least you can do really. Ear plugs can be bought in bulk from B&Q, as can other bits and bobs, to negate the impact a bit.
We've done long car journeys with 2 children, at various ages, no opportunity to get up and walk about unless stopping for a break. They managed to cope fine, I was prepared for all eventualities, some may say lucky you, but it's obvious our sanity relied on the children's behaviour, during occasions such as traffic jams which were tedious for all involved.
It makes me sad that people have this, 'well what do you expect?' attitude. I'm sure many would reply manners and courtesy. At least an apology, rather than building your own victim complex that you're the poor soul with the small child. (From the post that stated she was ready to let rip at the woman tutting!)
On a lighter note, OP, if you encounter this again, with a sole child being allowed to run riot, get a couple of packs of condoms from a vending machine, offer it as a gift to the parents for future passengers sanity. If they offer no apology, at the end of the flight offer it in a cheap gift bag with a note, saying, a mere suggestion seeing as you were unable to control the behaviour of your child/children on this flight, for the sanity of future passengers you may encounter. Have a happy holiday.