My arrangement with my parents before and upon graduating from college was that they would lend me money when I needed it and I’d pay them back later from my job. Similarly parents in law lent us money for part of the downpayment on our first home and we paid them back afterwards with interest. But later on when my parents were better off in retirement they would take the whole family on vacation (mostly cruises which they really enjoyed) and pay for food whenever we went out. They also gave money to each grandchild to help with college costs.
We’ve done something similar with our kids: they have a certain amount in 529 money plus money they’ve been given by grandparents etc over the years, managed by us (we credit them with interest). We added to that if one kid gets something the other doesn’t (eg one took our old car, so we credited the equivalent value to the other kid). Likely the same will happen with weddings etc. They can withdraw from the bank of mom and dad when needed (and we’ve pushed them to do so for things like Roth IRA contributions). But we also let them use our hotel points and airline miles whenever possible for trips, job interviews, relocation etc. And the expectation is that we pay when they are with us and we eat out, travel, etc.