Growing up, my parents took us on a big trip each year...to Disney most years, Grand Canyon, Washington, DC, wherever. My sister and I never paid for a thing, ever, except for souvenirs we wanted and they refused to buy - like stuffed animals, ha! (After age 9 or so, they were on me because my mother deemed them "dust collectors"). Even when we traveled with them while married my parents usually pay. I plan on handling things as my parents do/did. Yes, there are fights about checks at restaurants, other expenses, and sometimes we beat them to the punch and can successfully "win" and pay.
We're heading to Disney next week for our 5th family trip there and our kids are 7 & 5. My 16 year old niece is also joining us. None of the kids will pay for trip expenses, even the 16 year old. Her "job" is babysitting my kids a couple days a week in the summer. She doesn't have endless money. My husband and I (or my parents, as they live in Florida for part of the year) will get her whatever she needs.
Having said that, my kids buy some of their own souvenirs. As part of a Christmas gift they were each given GC to Disney. They are so excited to make their own choices instead of me saying, "Really? You'll never play with that!" Their gift card, their choice....as much as it might pain me. Ha!