With both kids we let them know what we could/would contribute. Child 2 actually had a bit higher contribution than child 1 since we had more time to save. IMO it is difficult to manage outcomes from of “cost of college” perspective because the kids are different. Kid 1 is an engineering major and because of scholarships and co-ops was able to afford an OOS flagship. D2 has completely different interests and wanted an instate school. She will not have the opportunity to co-op so her financial options were more limited. In the end they will both go to schools which provide them the opportunity to thrive in both their fields of interests and in those areas they enjoy. Both kids were limited by what we could provide and where they were given scholarships. One is at a school that is around $43k/yr and the other at a school which is around $25k/yr. The great news is that both are at essentially there top choice school.
Glad to see this thread as I am in a similar situation, but contending with several children spanning 10+ years apart!
Son 1 chose an Ivy and we are paying a good bit. It hurts, but we are making it. He works his tail off to help bring down the costs, including being an RA to eliminate all room and some board. He earns all his own spending money.
Daughter 1 chose a full ride and turned down and Ivy and some top LACs. She works her tail off to maintain that scholarships. We are paying almost nothing during the academic year (even her books are covered), but have given her help to travel abroad in the summer and do an unpaid internship. Still, she is costing us substantially less than Son1. We do wonder whether we should plan on giving her $ toward graduate school.
Both are where they want. He LOVES wearing his Ivy gear and feels a sense of pride in accomplishment with it, and does like the school and the bright student body. She loves her school, honors program, a diversity of student levels and lack of financial stress.
We also have 2 more soon to be heading to college, and then a couple bringing up the rear. I see no way to be ‘equal’’ with these kids, but do want to be ‘fair’.
I will say, my younger ones (high schoolers close to college age) feel that their sister made the better decision, given the opportunities she has had and the lack of stress financially on her shoulders and the vibe of her school. So, in the end they may choose to make very, very affordable choices that will mean for them no loans and some wiggle room in the summers. But if not, how much to ‘help’? Obviously, it will be impacted but what we CAN do (we will not take out parent plus loans as we have great state schools as an option) realistically.
" Obviously, it will be impacted but what we CAN do (we will not take out parent plus loans as we have great state schools as an option) realistically. "
Then THAT is the premise you tell them to start with.
Tell them that given how much college costs have gone up recently, [and you have to assume they will continue to do so], they will need to choose colleges that wont cost any more than the state schools cost.
They and you will need to run NPC’s and look for colleges costing the same or offering merit scholarships if they want to go to elsewhere.
I think you pay as much as you can afford for an educational experience that you want your children to have and you decide what is and isn’t a perk. With that said, it’s possible that the “perks” of the first son’s success will continue throughout life. Will you continue to “equalize” their life experiences if that happens? This is probably off-topic, but something to consider.
What is “fair” is that you will find a way to provide a college education for each child within the established budget, and do so in a way that does not jeopardize the younger siblings’ opportunities. If the budget is the EFC, then that’s where you draw the line. You’ll help each up to the EFC. And while it’s fine to allow more educational “perks” during the college years for the kid who took the great FA package and came in under the EFC, at some point you stop trying to equalize. For me, I’d set the stop point around college graduation.
@MotherOfDragons - too late . . . I am already a burden to my kids. They remind me frequently. 
We have planned so that we can pay for up to a U of MN education for both of our kids. That means they can attend any branch of the university and all of the state colleges fall into our price range too. We have reciprocity with ND and WI public schools. A lot of affordable public options are available to them. My oldest daughter wanted to attend a private school that would normally be above our budget. She got a large merit award from them and also received a large four year renewable scholarship award that puts it in line with our state schools. We feel like we are getting a lot of bang for our buck. Our second daughter will have the same deal. If she doesn’t have the stats to earn the merit awards like her sister, she’ll still have a lot of good college options available to her. We feel like our plan is fair. Fair doesn’t always mean equal.