We travel with DS14 and DD11. I have a family of complainers. My son is our biggest offender due to added issues of ADD, OCD, etc. 
On our last trip, we created "The Eeyore Award". I bought a small plush clip on Eeyore at the park. His 4 legs are magnetized so he can be attached to purse straps, etc. Whenever someone said something negative or complained, they had to wear Eeyore.
He was clipped to hat brims, fanny pack straps, shirt pockets, etc. Eeyore stayed with that person until someone else "earned" him.
I was surprised at how well it worked and realized that sometimes we don't even realize how many times we complain until it is pointed out to us. I was very surprised how well it worked with kids this old too! Just being awarded Eeyore usually brought a smile and a mood change. Even worked on DH and, yes, even me.
I highly recommend it to keep your vacation positive!

On our last trip, we created "The Eeyore Award". I bought a small plush clip on Eeyore at the park. His 4 legs are magnetized so he can be attached to purse straps, etc. Whenever someone said something negative or complained, they had to wear Eeyore.

He was clipped to hat brims, fanny pack straps, shirt pockets, etc. Eeyore stayed with that person until someone else "earned" him.
I was surprised at how well it worked and realized that sometimes we don't even realize how many times we complain until it is pointed out to us. I was very surprised how well it worked with kids this old too! Just being awarded Eeyore usually brought a smile and a mood change. Even worked on DH and, yes, even me.

I highly recommend it to keep your vacation positive!