I think so?

Anecdotal here, but skid was 6/7 years old here. Old enough to register the major shifts that were going on in her life. Old enough to register the emotional turmoil her mom was exposing her to. 

With that said, skid is currently in therapy, and has been for a few years, to navigate all the feels. 

Part of me is happy, because I’m a huge proponent of therapy. The other half is indifferent and leery, because I have zero doubts it’s a manipulative tactic on BM’s behalf. 

Adding: VERY early on, skid was very hopeful that DH and I would start including BM on “family time,” etc. Or rather, skid thought I was just a temporary fill.

I have found the opposite to be true. SD is 6 now and her parents divorced when she was 18 months old. 

She really has not shown any inclination of any fantasies of a reunion. Her BM remarried and SD loves her stepdad (much to our disdain but that's another topic). 

And SD loves me too. Tells everyone she has two moms. Regularly refers to herself as my child. She's also called me Mommy which I neither encourage or discourage. 

I don't think there is a cut and dry answer here - it depends on the kid's personality and on the parents. 

BM and DH split when SD was 9 months old. BM refused to see SD until she was 2 years old, then she decided she'd take her in the summer. DH and I have been together since she was 2 years old. She doesn't remember a time where I wasn't in her life, so every once in a while, she'll forget that I wasn't there before and ask a question about when she was a baby or something and I have to remind her that I don't know :-) 

She went through a phase around 3-4 years old of wanting her mom and dad together. She would make comments like "why can't mommy move in?" or if we were in the car, she'd say "I wish mommy and daddy could sit together in the front while I'm in the back" (how rude lol I was sitting in the front with dad!) but I thought it was odd because she'd never actually seen them together. 

I think she was starting to realize other people have moms/dads in the house and she didn't see me as a mom at that point because I was fairly disengaged. Within a few months of that phase, she told me she wished I was her mom and started calling me mom. I think she's made a couple comments here and there over the years, but more asking why she has a stepmom/dad instead of a mom/dad living with her. Or asking why she has two moms in her life. 

We try to remind her that she's lucky because she has even MORE people in her life who love her, but who knows how she really feels? 

My YSD was 10 months when I met DH and is 23 y/o now and still wishes her parents were together. She only told me as a kid 4 or 5 "I wish you and SDad was married and mommy and daddy was married" but has said/did things just 2 years ago to confirm she wants them together.  Ex. we (dh and i) went back home for my FIL funeral and at the repass she made sure her BM sat at the head table with us and when BM went to the restroom YSD checked BM's text messages without BM's knowledge (BM left her phone at the table and I sat there and watched her), then later that day told me she thinks my OSD dislikes me because "she thinks because of you my dad and her mom will never get back together" (2 BM's) but I've never got that impression or confession from OSD and she knows her parents can't stand each other. Then when we got back to MIL's house YSD was going through boxes of old photos,  sorta like a maniac and showing DH pics of he and her BM (one prom pic and one other pic when they bought her home from the hospital). So to answer your question,  I think so. 

YSD is even the most well balanced and respectful one of the 2 SD's but she definitely resents our bk's (no contact for the most part) and sometimes throws small jabs meant as a joke towards me and has compared me to her BM a few times over the years. 

ETA: She has grown to accept and love her Sdad and I since she only know of BM/SDad and BD/SM.

My SS was 14 or and at 16 still told his dad he thought they'd get back together at some point.

Oh, and if it helps, I am 24 and my parents divorced when I was 15. I STILL wish they'd get back together. They sucked when they were together because they got into the cycle of not appreciating each other/their relationship and not being the best individuals they could be. So seeing them with new spouses being really great as individuals makes me wish those great individuals could be together. I think they'd have a way better relationship now. But that's probably hopeful COD thinking LOL. 

Also as a more personal anecdote. I was 21 when my parents divorced, ha. And the feeling and fantasy of wanting them back together remains. 

SD6 was 3, approaching 4, when DH and BM split up.  She remembers them together, and when she was 4 and 5 she would make comments about them getting back together.  She hasn't done that in 18 months or so; instead she started saying that she wanted a stepmom and a stepdad (which I thought was odd, but whatever).  SD4 was 1 at the time they separated.  She has no memory of her parents living together; DH and I have been together longer than she lived with DH and BM together.  She has never once mentioned them getting back together, even when her sister was talking about it.

Of course, I only know what they say out loud, I have no idea what else might be going through their little minds.

my middle child was 17 months old and oldest was barely four so one never knew us together and two don't remember. In my experience they have no fantasy whatsoever of us getting back together 

Could be true. My SD is 11, her parents broke up when she was 1, DH and I have been together since she was 2, and she still has that fantasy they will all be together (even though we’ve been married 7 years and have kids together now). 

when their dad moved out and about six months later DH and I entered into a relationship (we had known each other for a couple of years though). So my DD doesn't remember a time where her stepdad wasn't around and DS barely remembers. They never expressed any desire for their dad and I to get back together. I have even asked them (they are adults) and they laughed and said no. It never even crossed their minds. They love DH and couldn't imagine a life without him. 

and they still go out of their way especially sd’s talkign about bio mum being so relevant.

they know the reality that they’re divorced but they go out of their way to talk about the good old times except there were none with bio mum

The SDs were 4 and 6 when the divorce happened. SD6 saw some terrible behavior by both BM and DH but BM was expert at manipulation. DH didn't get regular 50/50 until they were 6 and 8. He's always made it clear there is no getting back together and no friendship. 

OSD used to want them back together pretty badly, until about two years ago when (I believe) BM likely came out to her. YSD has never once said it, I think she's ok with her life overall.