The Good Adoptee

I have a question for you and would appreciate any insight. Is there such a thing as an adoptee being too good? 

What I mean by that is, is it normal for an adoptee who was recently adopted behaving too good? A child who never complains, never asks for anything and is always polite. I came across this description in an article I was reading about a couple who adopted 8 kids. What jumped out at me whilst reading was how pleased they were that all the kids were happy, well behaved and polite and that none of the children made demands, infact they were all rather quiet.

I could not help but reflect on my own adopted cildren and noticed that the ones that were adopted older fit that same description, but the ones I raised since birth...did not. Infact, the children adopted as newborns (who are older now) make their feelings and wishes known very loudly to everyone around them.

I would appreciate any insight any one has as to what emotionally and psychologically is really at play here or the rationale behind this. Thank you in advance for the replies.