Hi excited, I may be off on a tangent here, and didn't see the thread you refer to about the 8 year old. But would suggest that the problems referred to aren't' about the actual fact they are adopted, rather the whole range of issues it brings!
I have learnt so much in the last 5 years I fear I am able to hold my own in discussions with the professionals and am at a better place in understanding why they do what they do (although I struggle sometimes to always be so understanding!).
When babies are in the womb, we like to think that the birth mothers look after themselves and put their baby first. However, in less than perfect situations, birth mum may drink, do drugs, be stressed, ill, all at one go. It is has been shown that the stress hormone cortisol can affect the unborn child and this can affect brain development. So whilst at 6 months they may not 'remember', their brains do.
Then when born, instead of the calm, rocking lullaby singing peaceful world we would want for them, they frequently lack basic care and skills. For the first 12 weeks of life, the key period, they need to learn that as creatures they are safe, when they cry someone will come, when they are hungry they will be fed, and will survive. After the brain understands this, and only then, does the brain development of a baby move on to trying to move and exist as an independent being.
My son did not have this calm period of time, either before or post-birth, and I can see his brain can't calm, gets anxious and constantly seeks attention to prove he exists. He was (probably!) born with increased cortisol levels in the brain, and which his brain thinks is normal. So as he gets older he has sought out ways to get the cortisol (similar to a drug addict!) and so when I shout or get cross the cortisol is released and he gets his fix. But we are working really hard on bringing his levels down and so far so good. I have the best relationship I have ever had with him and he is doing much better. All because I now understand that his behaviour isn't just him being 'naughty' but because his very brain pathways are different. But they can be changed and built, and it is a question of going right back to basics and making him feel safe, secure and loved and then moving forward with all the other normal child development stuff.
Sorry, gone on too long, but I found I was able to cope with all the 'adoption' things I could see and am open with them about their early life experiences, but I have become a better mother because I understand what they need from me (and the world!).
Good luck x