I never understood that elves are less attached to their children, really... they are 'human' too after all. It is mentioned, however, that elven society doesn't make difference between educating a boy or a girl (so non-sexist education is called 'the elven way').
I know this is slightly off topic for a screenshot thread...
Just my 2cents on this. I don't think they are less attached to their children, even if their children eventually wonder off more.
Once again, we're back to talking about lifespans. If the average human lives for about 50 years. You reach sexual maturity when you are 15. Let's say you have kids between then and until about 25, and each kid would stay with you for about 15 years as it grows up. By then you're about 40 and in about a decade or so you'd be dead.
So essentially, a large proportion of your life is spent growing up with your elder family, and an even more significant part of your life is spent raising your children. And that doesn't leave much in between or after.
If we say that elves spend 15 years growing up with their parents too. Then an elf with a lifespan of 300 years spends about 5% of that growing up with their parents and maybe 5-10% of it raising their kids. All the other time, they are not dependent on their parents anymore and are not raising kids. I think they just have more freedom when they are not needed to be part of a family unit.
But... given their long lives, elves I'd imagine would have much longer relationships with others and their families. I don't think they'd be less attached to said family. But rather it'd just be more culturally acceptable to do drastically different things to your family, go to different places, etc.