Ok, Here it is. My personal story. I hope this helps you a little. Kids are amazing, and can figure out how to handle these things if we give them honest answers, in little increments, as they can deal with it at age appropriate times. Here it goes.....
We got custody of our 4 yr old nephew and 2 yr old niece a little over 5 yrs ago. (they are 7 and 9 now) When they came to live with us, they had never met us, and we were intoroduced as aunt and uncle. We also had 2 teenage daughters. They had been living with various family members for short periods of time, passed around from home to home. Our nephew, (the 4 yr old) did remember his father, and our 2 yr old niece seemed to as he was the one who actually brought the children to our home to live with us. (a quick 3 days visit and drop off) The 2 yr old did not speak when they arrived, so as she learned to talk, she copied our older kids and called us Mommy and Daddy, although at times she would call my husband daddy "---------" (insert his first name there) The 4 yr old called me by my first name and my husband by his first name as well, not even using aunt and uncle, as his speech was very bad too. (we were just happy that they were calling us anything) After a while our nephew began to refer to us at preschool as his "mommy and daddy", but still never called us that. One day he called me Mommy when he got hurt. He has always known that he had another Mom, (who he never sees and lives in another state), and another Dad. He just understood that he lived with us and we were going to take care of him like a mommy and Daddy would care for their own kids. I told him time and time again how lucky I was to finally have a little boy to take care of (I only had girls up to that point) and that he was a blessing. At night when I put him to bed he would tell me he was a lucky boy, and I would tell him I was a lucky Mom. One night, about a year after he lived here, he asked me if his other Mommy was dead, (she never called) and I said no. She just lived far away and coudn't see him or call him but she loved him very much. He asked me if I was his MOm now, and I said I was doing everything a Mom would do for him, and would love him as his Mom, but that he was a special and lucky boy because he gets to have 2 mommies, and 2 daddies, so he was especially lucky. He asked that night if he could call me Mommy. I told him he could call me whatever he would like to call me. From that next day on, I have been Mom. He said it about 80 times an hour the next 5 days, and worked our daughters into the setup as his sisters. The girls had come up with cute names like brouzin and cister. LOL! They were all aware that they were cousins who were living as a family, as siblings. They love each other UNCONDITIONALLY and would do anything for each other. The big age difference with the kids has been a blessing in that it actually is like having another set of Moms at times. My 20 yr old volunteers at school, and both girls have been girl scout volunteer leaders etc. These kids are getting the best care possible now! There is so much love available to them. My girls have learned so much, including that they in no way wanted to get pregnant and become teenage parents. (good one for me and the hubby!) A side note here, is that BOTH of my additions are special needs children, so they may have had a tougher time with the understanding of family dynamics. They have done wonderfully. Their bio dad has pretty regular phone contact, and does come for visits and occasional overnights with them. He is the "other Dad". My husband is their "real Dad" since he is the one they live with. Those are their words. My niece even did a paper at school once and had to draw a photo of her fav. uncle and drew her other Dad. I told her it was her Bio. Dad, not her uncle, and she said, "no, the teacher said your Uncle is your Mom's brother or your Dad's brother... so it's my uncle Daddy! " I have it hanging in our kitchen to this day! (their father is my husband's brother) There is quite an age difference between my husband and his brother, and I have photos of him(his brother) and myself when I was 18, and I showed the kids one day when we were looking through old family photos, and my niece asked me "oh, is that when you married our other Dad?" I had to re explain that I never married her other Dad, because she was under the understanding that to have them I must have married her other Dad too. LOL! I explain that her other Mommy had married her other Dad and had her in her belly and then they came to live here when they were older, and I have been the happiest I could ever be ever since! She gets a little confused at times, but it's worth it. She will never feel lied to, and she will totally understand someday. Their bio Dad tries to help too. (with the explanations) We don't tell them the reasons why they are here, except that we could take better care of them, and their parents loved them so much that they wanted them to get the best care they could, even if it meant missing them every day. The funny part is when I have parties and both Dads are here and parents from school jump to conclusions since I am the only Mommy, and think that I had my 2 older girls who are now 17 and 20 with my husband, and then had an affair with his brother and had my 2 younger kids who are 7 and 9, and then went back to my husband. Ok, yea, I am not Jerry Springer material here! LOL! Come on people! It's humorous! I say go with the truth. It's always the best! Do it for your whole family, and for yourself. You don't ever have to worry about what you said if you told the truth. Lies can come back to bite you, and hurt everyone. Please, the kids can handle it all. Even this young. All except for any painful reasons that they may take as their fault which are NEVER their fault. Keep those to yourself. Good luck. I don't usually share this long story in such a public forum, but it seemed like maybe the right time and place. I hope it helps you even if only a little! I wish you the best!!