I have never been on a flight that I had to pay extra for securing seats on, seriously! Who would do that? Can you not see that it is just a way to make your part with more money?
If I didn't gets seats with my 4yr old & 9 yr old, this would happen
9 yr old would sob uncontrollably the entire flight, between vomiting & asking for her parents, because well, you know, some kids like to be with their parents, cos like, it makes them feel all safe & shit!
4yr old would would start off upset, throw an almighty fit & then realise that this is actually a great thing because she can do what the hell she likes & she bloody well would! Including talking to death who ever was next to her & probably climbing all over them & kicking seats (not that she does that normally, but tell me, how many unsupervised pre schoolers are going to sit nicely?)
You would probably end up with your dinner on you, perhaps your drink too oh & hers too. And make no mistake that she will order coke & sunkist (no, she isn't allowed them) & be on a sugar high for the whole time (oh & she would probably vomit too as she has no idea of when to stop eating)
You would also probably have to move several times for her endless desire to see use the toilet, because she can. But you can't ignore this, because you will have NO idea exactly when she does need the loo (& it could happen at the point that she is climbing over you). If you don't oblige & move, she WILL climb over you/your legs to get out. Also, she will relentless put her tray up & down & the people in front of her will think she belongs to you & be pissed off with you! Oh & good luck if she wets herself!
After a while she will get bored & want you to play or have you read her book. Try saying no...go on, I dare ya! I bloody double dare ya in fact! 
She may sleep (although she didn't on a 13hr flight from Dubai - Australia) so you might get some peace.
When we are at our destination, I will come get her, and tell you that I hope the entertainment was worth you being precious over your seat! I of course, will be thoroughly refreshed & clean, tidy & ready for my holiday. You might not be.
But if you like the idea of that, I hope I get you next time I fly Australia - London. 


