I've heard the term "The Stepmother's Dilemma" applied toward that moment when you have to decide whether to count your step-child among your own (and risk sounding like you're trying to replace his mother) or accurately call him your step-child (and risk making him feel less important/loved than your biological kids). Since there's a term for it, you know you're not alone in worrying about it!
As a rule, if I don't have a significant relationship with someone, I tell them I have 4 kids and call my step-son my "son". When a person isn't asking for/interested in my whole life history - they're just politely inquiring whether I have a house full of kids or merely one or two - I feel mean, if I make a point of clarifying that my step-son isn't "mine". If someone is close enough (or grows close enough) to our family that they might meet my step-son's mom, or hear him talking about her, then when an opportunity arises, I'll clarify the relationships. For example, if I'm discussing winter break plans with someone, I might say, "The twins vacation with their Dad and Step-Mom the week after Christmas and (Middle Child) visits his Mom in California then, so that week's always very quiet at our house. We just have our baby at home with us." That gives the person the opportunity to say, "Oh! I didn't realize (Middle Child) was your step-son. I always see him with you, and you're always at school volunteering. I just assumed you were his mom." Then I can explain, "Well, he lives with us and I feel like he's one of mine. But his real mother is in California."
At a recent Back to School Night at one of my kids' schools, there was a newly-married couple. She introduced herself to the group of parents, stating who her daughters were and what grades they were in. Then it was her husband's turn to introduce himself and he said, "I'm (Fred). (Judy) and I were married in (June), so now (Jane) and (Jenny) are my daughters, too." It was so sweet. No one had time for (or wanted to hear) details about why Jane and Jenny's biological father wasn't there, or how he felt about Fred calling them his daughters, without the "step". No one assumed Fred was aggressively denying Jane and Jenny's relationship with their "real" dad. We all knew Fred was "only" the step-dad, but everyone understood that, by calling the girls his "daughters", he was simply embracing the entire family he had married into and establishing that his new role in his step-daughters' life was very important to him.
That reinforced to me that reasonable people won't judge me, if I call my step-son "my son" and later - if a conversation requires it - clarify the "step". Whereas, if I always clarify the "step" - even when it's not necessary in the conversation - people might wonder why it's so important to me, to make sure even strangers know my step-son isn't "mine".
Now, if I have a friend (even if she's not close to the rest of my family) with whom it would be nice to discuss the stress of going back to court with my step-son's mom; or the frustration of having all the responsibilities of "Mom", yet being treated like the evil stepmother when I call my step-son out for not doing his homework... I don't hesitate to clarify the relationships. You should never feel bad admitting that you're the stepmother, if it's germane to the conversation. You mention a relative stranger asking about your pregnancies. At that point, I don't think there's anything wrong with clarifying, "Although I do have 4 kids (like I said before), the middle one is my step-son, so I've only had 3 pregnancies."
It's developmentally normal for kids in the age-range you describe to be unclear about family relationships. Even in a nuclear family, if the oldest sibling is significantly older and has been away at college most of the youngest sibling's life, the youngest sibling - even if they adore the oldest one - may need to be reminded that Johnny is their brother and not a cousin, uncle or family friend. So imagine how much more confusing it is, for a young kid who has step- AND half-siblings. And it's doubly confusing if there are step- and/or half-siblings at both parents' houses. Naturally, it seems very clear to us that Sam has the same relationship to his Dad and Step-mom's baby as he does to his Mom and Step-Dad's baby. But that may be a legitimately confusing concept, to him. Naturally, our feelings are hurt when a kid seems to reject or downplay his relationships with us or our kids. But:
A) He may not mean anything negative by it. Perhaps he's still trying to work it all out in his head and it just hasn't "clicked" yet.
B) His mother may be encouraging him to think he has closer relationships with the other kids at her house than he does, with those at his Dad's.
Our youngest (let's call him "Jack") is almost 5 and has a lot of confusion about "brothers". My husband and I call all our sons "brothers" and don't bother with the "step" and "half". But from Jack's perspective, it's legitimately quite confusing!
A) Two of his "brothers" look alike, are the same age, share a bedroom, and frequently go together to visit their dad, step-mom and two younger half-brothers. Jack has little to no clue about all those relationships and calls all those people by their first names. Also, HE visits them sometimes, too, even though he knows for sure that they're not HIS parents or brothers.
B) Another "brother" shares a bedroom with Jack and spends nearly all his time at our house, like Jack. But every once in a blue moon, that "brother" leaves for what seems like an eternity, to visit someone he calls "my mom". Jack has never been introduced to this other mother and suspects that her existence is some sort of joke or trick; that of course I am the only Mom any of them have.
C) My husband is older than I am and also has two sons from his first marriage, during college. Both of those "brothers" are grown, married and don't live nearby, so for the most part we see them on the same special occasions when we see aunts, uncles and cousins. Plus, in Jack's eyes, the oldest of these "brothers" seems older than my husband (I think because of his linebacker build). How can a man Jack perceives as bigger and older than Daddy be his "brother"?
Jack often dismisses all this confusion by insisting that only the twins are "brothers". There's no denying they're a unit! Sometimes, he has claimed he and my step-son are twins, too, because they share a room. But obviously they don't share as many similarities as the twins, so he doesn't stick with that theory. Usually, he declares that NONE of them are really "brothers", except the twins.
I consistently reinforce that they're all brothers; that you don't have to be twins or share a room or have everything in your life seem the same, to be brothers. I also remind him that it hurts the other boys' feelings when he tells them they're not his brothers. I acknowledge that he may just be confused and not trying to hurt anyone's feelings, but when his brothers hear him say that, they think he doesn't want to be their brother. I ask him to think how he would feel - knowing I'm his mom - if he heard me say that I wasn't? I also let it roll off my back and remind our older 3 not to take it personally. But your step-son will take longer to figure things out, if you don't explain them to him and "let it go" when he's confused.
Edited by VocalMinority - 1/11/13 at 5:05am