SD - I don't know the answers. BUT you have done a wonderful thing - given someone one of the greatest gifts that there is.

I think that maybe when your children are 12 or 13 you can explain to them that you believe in helping others which help comes in all sorts of forms of help. And in your case it was giving someone some help making a a baby. And that baby was so wanted and so loved. And that baby is the child of its mum and dad (or who ever) and has its own family that loves the baby as much as you love your children and who loves its mummy etc. as much as your children love you. So although they may share some dna they are not part of your family.

I do think the wanting to meet makes things more complicated but not necessarily in a bad way. From what I've read and been told this probably won't be the big deal that you anticipate. Not to say that it is not a big deal but probably not because of the reasons you are worried about.

PS - just because you tell your children doesn't mean you have to tell relations and friends. It's a private matter - you don't need to share it with everyone.