How do you tell them? As the perfectly reasonable choice it was for you. Presumably, "I wanted more kids but couldn't grow them in my own body, so I paid this wonderful lady to do that part for me. " They'll want to know (I do not need to) whether you used your own genetic material or not.
There's a wonderful poem about adopted children -- "You didn't grow under my heart, but in it". Still applies.
I just read your other post, and am vague about the age of these kids. This rather matters, as does the risk of them finding out by accident or getting the wrong story from other relatives. If there's a risk, you'd really rather it came from you first. It probably helps that their cousins are adopted.
My oldest biological son is in his twenties, the other two are in their early teens. It helps that my son who is getting married will be the father to his wife's child by another man. This at first gave me pause. But now I see how wonderful he is with the child. Also, my other children like having more of an extended family. I now feel it will work out. Thanks.
