I can relate to most of what you wrote--I turned 42 yesterday--and my children are special needs and it often shows in public situations... I am Irish the children are much different looking then me---but not completely--It can be hard when we are out because people will say, "You must get those brown eyes from your daddy"--and of course considering the fact our daughter was not our daughter until she was 5 years old--that brings out the fact that we Adopted her...and then questions and then people thanking me right in front of my kids for the 'wonderful things we are doing"
Being a 40-somthing mom has been interesting in itself..... It really can be very difficult to 'fit in with' the younger people.... My lucky thing is that I have my older kids both before I was 22 so I used to be one of those YOUNGEST moms in the group and I understand how THEY feel about me today.... When my older kids were in grade school I remember one of the mothers was quit older then me....I am thinking she must have been in her 40s back then and lived a life of established success... This woman was soooooo nice to me and reached out attempting to connect with me for YEARS.... But I was so insecure with my own life that I felt like she was attempting to mentor me or something and NOW I really do regret the way I responded to her.
It is not only the fact we are the age we are--It is that our wisdom sticks out and those younger parents do not know how to treat us as equals.... It really is not all their faults because they just don't feel up to us... I don't believe they are looking down at us...I think we intimidate them and they feel like we KNOW too much to be part of their groups.... Like some old Aunt or Teacher butting into their conversations. I mean how on earth could we understand the issues in their lives because clearly we are more successful and we have done more in our lives...and after all for you and I we adopted kids....that must take some big bucks and some really great life....
I also think that in general when we hit those 40's years we as a population are finding it more and more difficult to MAKE NEW Friends... Add to that the fact that you and I are parenting younger children then the majority of parents with kids our age and well...... it can be difficult to connect to anyone.
Then we don't have the stories of how we gave birth.... I have always been sort of used to this being left out part because my older children were C-sections so I never got to --
push--and never had that part of the story to share--or all the rest--and usually didn't have much to say in the labor and delivery conversations... But I had the recovery things and well, the only people who wanted to talk about that had C-sections too....which thank goodness is less often....
It has taken me a little while to GET OVER my own feelings of being left out.... and I have just learned to smile and nod a lot in the situations like you have been facing. Sometimes I have decided it is NOT worth my while to keep putting myself into situations that make me feel uncomfortable---and sometimes I have decided that maybe I am supposed to help CHANGE the attitudes of other people...by not allowing their attitudes to upset me...and by showing that my kid and myself are JUST the same as they are....just that our family was put together differently...
I had really terrible problems with getting my daughter into Girl Scouts.... Ten years ago I was a big wig at the council level--editor of the news paper and served on several important boards in the regional area--when I called last August to get back in the young new people there were all about how things have changes so much since my ancient history! That I would need every level of retraining and that I couldn't possibly know anything about Girl Scouts in modern history!

Only Two significant changes have happened--and I was on the committee that started the research to implement one of them.... They look at me like I came out of the past and haunt them to death... I will not need to be retrained...thank Goodness there is a National Level and ONCE a Girl Scout Always a Girl Scout and leaders are leaders forever--we just need a recent update to CPR and First Aid and it is suggested we take a brush up course on basic training to catch on to new things and remember what we might have forgotten....

.... and a recent criminal history but everyone has to do that so many years apart...
So THERE!
But then I realize when I got beck in that one of the new big wigs was once a Girl in one of my Troops! So there! Right back at me!
Just remember that EACH person in this world has a story and that it is NOT always US with the issue--more often then not it really is their problem and if we pull back and don't keep on keeping on they win! And we go home feeling bad!
I have decided that I never really did like the whole play group thing even when I was a young mom--It was way too much like High School to be among the group of my kid is better then yours... Even when my older ones were in these kinds of groups I personally had my own feelings about dealing with Mary and Jane who made everything from scratch and had the smartest 3 year old God ever placed on earth...So this time around I decided that Play Groups would not be something I got into...I make the play group at home...and pay for two mornings a week of preschool for my little one--that way I can take an aqua aerobic class and work out the pain from my arthuritis....with all the 60 year olds!