Hi OP,
It's so far so good for us. We have BC (aged 5), BC (aged 3) and AC (aged 1). AC has been with us nearly five months, so yes, still early days in the grand scheme but I can't say there's been any 'negative impact' on BCs as yet. I think that introducing any sibling, adopted or biological brings out questions of 'how might this negetively impact my exisiting child/ren'. We actually found ourselves asking whether we were 'doing the right thing' more often when pregnant with BC2, rather than when in the adoption process for child 3, as having multiple children was such a step into the unknown for us at that point in time.
By contrast, when our AC came along we were very chilled, as we felt like really experienced parents (of that age child); we'd coped with sibling jealousy before, we'd seen that BC1 and BC2 are polar opposites (despite being biological siblings), and so AC was just simply child 3 for us, no great expectations of our DC3 'rocking the boat' based on being adopted, just expectations of family dynamics possibly changing for a bit, because that's part of the course.
hmm...I don't think I'm helping with your quandry any here, so I'll move on to your request for experiences of the differences between parenting both BC and AC.
When AC reaches milestones for the first time, such as saying 'mummy' and walking I feel extra proud.
When AC gets a bruise or bash from tripping over, or a virus- a cold or stomach bug etc, maybe I worry just a little bit more than with BCs, simply because I'm still not sure how great ACs immune system is compared to my BCs, as I didn't 'make' DC3's immunity...if you catch my drift.
I find that when the BCs fight with each other or are affectionate to each other, friends and extended family don't tend to comment, but when BCs kiss and cuddle AC, and occasionally snatch DC3's toys, friends and family pass comment...(I think this is still because AC is fairly new, but time will tell on that).
...I'm wracking my brains to think of other differences...
One poster mentioned discipline techniques being different for AC. Yes, I agree that it will be detrimental to use 'time out' etc for AC, but then BC2 is much more sensitive than BC1 so we've found we use different discipline techniques accordingly anyway. BC2 would scream in despair given a 'time out' so we just wouldn't do that, whereas BC1 really does respond well to 'time out' techniques, needing time to calm down from a rage.
Our expereince (so far...I appreciate that we're not 'experienced adopters' yet and we've only got very young children) is that there are more similarities than differences between parenting AC and BC. Feelings of love, adoration, frustration, curiosity, irritation...day to day parenting feelings, all the same. The need for routine (or some semblence of a routine at least), feeding, toileting, encourgaing and stimulating opportuinities for play, setting rules, maintaining a safe environment- all the same.
I really do apprecaite and listen to, on these boards, what adoptive parents with older children have to say on the 'differences' issue, as I'm sure further down the line differences in our family dynamic might be more pronounced, they're just really not here in any anxiety causing way at the moment.
Going back to the 'negative impact' on BC point again, what about the huge positives? The adoption process has encouraged us to be very open and honest with our BC about emotions, and we've learnt a lot about the way we parent, we've read up on child development issues (such as attachment) that I'd never heard of (that's definatley helped us understand BC1 a bit more). The adoption process has given us this amazing insight into the warmth, resilience, and thoughtfulness of our BC; they welcomed and accepted their adopted sibling with bundles of enthusiasm, excitement and a bit of apprehension. It was an amazing experience and I can't wait to talk about it with all the children when they're older.
I appreciate that our family dynamics will be ever changing, but just to share with you our current state of play: BC1 and BC2 are best friends (who squabble); BC1 and AC have a fun, loud and affectionate relationship involving endless games of chase (BC1 dotes on AC); BC2 and AC (just 21 months apart in age) were slightly jealous of each other for about ten days during initial placement; now they are very calm and contented play companions and share a love of dress up.
Best of luck with any decisions about potential adopted or biological children that you might make in the future.