How am I supposed to say good-bye?

Since December 2006, I've been fighting DHS- to keep my kids out of foster care, to get them home from foster care, to keep them from being put back in foster care, and to keep my parental rights from being terminated. The whole time, my now ex-husband was dead weight at best, actively working to sabotage me at worst.

So, it's finally come down to this. My parental rights were terminated yesterday, I get one more visit with my kids to say goodbye, and then they'll be put into a pre-adoptive placement. I've still got an appeal, but my chances are slim. I'm not sure who will adopt them- their paternal aunt has been circling like a vulture since she heard there was a chance I might lose them, she's still mad at me because I could get pregnant and she couldn't, so she thinks it's fair that she gets to steal my kids. She lives halfway across the country, has only met them a few times, and didn't have much interest in them before she saw them as a chance for her to be a mommy. I want them to be adopted by their former foster parents, who know them, love them, live in town, and would allow some contact with me. The other possibility is stranger adoption, which I see as a risk, but probably better than their aunt.

I think I should tell them they're going to be taken away and adopted by a new family. My son is 7 1/2, my daughter is 5.  I know he'll remember me, and I'm assuming he'll be able to find me online within a few years.

Oh, and one ironic detail is that DHS knows but does not seem to care that I'm part of a household with children. I can't see my own kids, but I can take care of other people's children no problem. So, if my kids do run into me in public, or find me online, it will be pretty obvious that I'm functionally part of a family. How would it feel to be taken away from your mom, and then run into her at the grocery store with her friends' kid? 

I don't know what to tell them. I plan to write letters to both of them that they can read when they get older, but I don't know what to say, other than how wrong it is. I'm also thinking about getting them some soft fuzzy blankets to keep them warm. He has a quilt I made for him, but it's in storage, and I still need to finish her quilt. I don't have time to knit anything new, although I could do some quick scrapbooks. I just don't know how to let them go, or what to do with my life for the next 10 years, or if they'll be raised to think I didn't want them or that I'm a bad mommy and I would have hurt them. 

If anyone has any insight, please let me know.