I've been very very fortunate as I have a lovely relationship with my parents and siblings. There's never been any fallings-out, no resentment (I'm aware of!) or anything like that. And when I boil it down it's because we knew that we were loved, and loved equally, without any doubts. Parents were (and continue to be) utterly fair.
I can't pin it down to something in particular they said or did, just that I knew from the earliest age that I was loved equally (or rather, it didn't occur to me that there was any other way).
So even though at different times of life the siblings have needed different help and support (financial, practical, child-care, emotional...) it doesn't change the fact I'm loved, we're loved. They might have had to focus more on one of us for a few months because of illness or some other problem, but they would have done the same for the others.
It's only as I've got older that I've realised the extent of which some people have favourites (and worse still show their favouritism), treat children and GC unfairly, and the issues that causes between siblings and the next generation.
If you trust in your parents completely that they love you and want what's best for you, it is such a gift - you have an inate feeling of worth that equips you better for life's knocks. If your parents don't show you that unconditional love and support, then it has the opposite effect.
Sorry, long-winded, but in short - show your children they are loved as the people they are, don't show favouritism, make sure they know you are there no matter what (while not pushing yourself in to their lives).