Myself and my db have had the same opportunities, I chose to leave school at 16 and go into an apprenticeship, I've always worked and now I own my own house, had kids later in life and have a good job that pays well enough for me to have luxuries etc.
My db chose to go to uni, he travelled a lot and has worked in low paid jobs since, he chose to have children earlier than me, and he lives in a v expensive place in the uk, and as such, on paper isn't as well off as me. Although both of us are lucky in that we are happy and healthy, as are our kids.
My mum used to try and 'help' my brother a lot financially, she'd arrange weekends away and expect me to help pay for my db and his kids, she'd want to give him money too, but thankfully my dad and my db would never agree to it, as it wasn't fair.
I suppose what I'm trying to say is that both me and my db had the same opportunities in life, we chose different paths, neither of which was the right one, but just because one party appears to have themselves sorted financially doesn't make it right or fair to favour the other when it comes to financial handouts.
A lot can change in a few years, parents can go into care eating away at all savings and equity in houses, financially stable children can experience ill health or redundancy. What's to say your financially stable child needs a 100k pay out in a few years time so they don't lose the their house, can you afford to do that in a few years time.
My Dad, as do I with my kids now, will never favour one above the other. If I can't afford two ice creams them no one gets one