We always said closed, closed, closed, no involvement whatsoever with the bios. After all, if they did enough damage that the kids had to be removed, we didn't want involved at all.
The exception would be involvement with siblings not with the bio family and maybe an occassional photo sent thru the agency to update them.
Our agency said with the last school photo that after S is adopted, they would no longer facilitate contact and we'd have to find new ways. I created a facebook page solely for bios. They are not safe to know where we live or where she's at, but kiddos's aunt is safe. We just don't trust that it wouldn't accidentally get out and be unsafe in the future.
I've been corresponding with the aunt, no location, no hints, etc, but sent a couple pics and let her know that kiddo is okay. Her aunt obviously adores her and kiddo adores her aunt.
Of her past, while kiddo typically pretends she's been here forever, it's always been obvious that her cousin and aunt are the 2 people she misses still, so kiddo was very happy to find out they're safe and still love her and think about her.
I kept waiting for a backlash afraid it'd trigger something, but almost a month and nothing. The bio mom doesn't have facebook anymore, so the aunt will provide me with address changes and I'll send yearly pics to her when we're out of town and the postmark doesn't narrow down where we're located.
I never thought I'd feel willing to talk to bios, but despite all the faults and problems, they did create this little angel and while part of my sending pics is compassion, it initially didn't start that way. The compassion developed later. On some level, early on, any photos shared was because I wanted it on some level obvious that kiddo is doing well with us.