- Just as an aside...I'm also a bit confused about the 12 year old, when you have 3 kids (8mo, 3, 5). A step sister? Half sister? Are there any other siblings that are yours by marriage?
Onto the topic:
If you take the masturbating out of it (which is still totally normal)...the subject of the q seems to be that she's taking her jammies off while she's in bed and pretending that there's someone else in bed with her. Yes?
I would be REALLY surprised if your daughter was actually taking this in a sexual way. Kids just don't take stuff there very often. They try stuff on for size, emulate, copy, pretend...but to actually be wanting sex...she'd most likely have a pituitary problem.
In a NON-sexual way...this could be:
- She wants something to hold and curl up with (I had a "pillow person" that I put a nightshirt over and would pretend that there was someone. I would also lean up against the wall as I slept...because it felt like it was curling up with someone.). It can be HARD to sleep alone. Most kids actually work out ways that it makes it "feel" like they're not all by themselves. Sometimes it's with stuffed friends, or a blankie, or an extra pillow, or pushed against a wall. It's not a sexual thing...it's a comfort thing. Especially if she doesn't have a lovie, or one has been taken away, she might use the only thing she can take into bed with her. Even if she IS allowed to take things into bed with her...I know I used a nightshirt because it "smelled right".
- She's copying her elders. If you ever wake up in the morning naked, or your husband doesn't wear a shirt to bed, or she's come in and you've rather frantically grabbed a nightshirt or robe or pulled the sheet up over yourself or said you can't get out of bed yet because you're not dressed yet, or you just LIKE to sleep in the raw; she may very well be copying you or your husband. You two sleep together (one is assuming), therefore if she's pretending to have someone curled up with her in bed who are her heros to emulate? Mum & dad.
- She's hot, but came up with an excuse that she thought would be acceptable (and rather had it blow up in her face). Lots of kids would rather go to bed naked (or just in undies) than to not have a blanket. Blankets are heavy, and comforting (aha, the word comforter just leaps to mind). I know lots of parents though who would rather pull the blanket/sheet off...than allow their kids to strip and sleep under a blanket.
- She has a bit of a sunburn (pj's are AWFUL on a sunburn), and came up with what she thought might be an acceptable excuse to avoid the "sunscreen" talk, or possibly not be allowed to do "x" the next day. Even if the sunburn is on her shoulders...ever gone to bed half dressed? Or taken off (like a wedding ring, or underwear, or whatever...something you have on all the time)? That wonky feeling can be unsupportable to kids. The all or nothing factor.
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In a quasi-sexual/non-sexual fashion:
Kids copy what they see and hear. This isn't news. It's why our non-squeeling toddler starts squeeling after hearing another child at the part do it. It's how ALL of us learn to talk. It's that cute moment when our six year old shows up in a tuxedo shirt and a briefcase (and nothing else), announces that he's off to work, and attempts to kiss us goodbye before walking out the door. It's how they learn sarcasm, the length of time appropriate for a familial kiss (remember baby smoosh kisses that you had to peel your face away from?), to nod when they mean yes, shake their head for no (that's reversed in some cultures...soooooo weird), not to look at other people's papers in school, how to flutter their eyelashes, and about a gazillion other things we take for granted every minute.
"Sleeping in bed naked -or without bottoms- with someone else" WE might take as sexual...but where did she come across it? I can think of a 100+ innocent ways. I know tons of kids who share a bed, and fully half or more pile in naked -or strip everything off over the course of the night- once summer heat hits. If these happen to be any of her friends from school/park/whatever...she might have decided to try it out. There's the story about how my grandfather broke his nose falling on his face because he was hopping around in the dark trying to get his boxers on to "scare off the burgler" that was my aunt sneaking in from a late date. It takes no leap of imagination to realize that if he was trying to put his boxers on, he didn't have them on to begin with! That he went to bed without his boxers (and that he slept with my grandmother) are not the points of the story...but kids pick up and focus on peculiar aspects. Any funny pants free stories in your family? Ours has dozens. Anyhow...literally HUNDREDS of places she could have heard about it. Then there's reading...even "night before xmas" has the narrator and his wife in nightshirts and caps (no mention of bottoms).
- Then of course, there's the fact that even though most 6/7 year olds hear the "snake in the jungle" & "car in the garage" euphemisms at school (although their actual grip or interest in this taboo thing varies, and usually isn't long lived...the opposite sex usually has cooties until puberty). Kids talk about things on the playground. They hide it (bacause they're told not to), but they talk about it. They play "boyfriend, girlfriend" or "husband & wife". It's play is all it is. Interest in copying their elders...the same way they learn about everything else. Do they REALLY want to be going to the office for 8 hours, just because they sit down and play office for 5 minutes? No. Not really. They want to THINK about it, play act it, maybe even go with mummy or daddy to their work (but that has more to do with wanting to be with their parent, than wanting to do their parents job). Kids try everything on for size. Does it mean that THEY actually want to be doing it? Not really. But they play at it, until they get bored of it. When they're told not to they either hide it (because it's just become REALLY interesting), or they feel ashamed...either of what they were doing, or merely of making mum and dad disappointed.
My son for awhile wanted to be a girl so that he could have "a baby in his tummy". Does that mean that he's gay, or a transgender candidate, or wants to be having sex? Nope. Just trying something on for size. He's not a girl, so he pretended to be one for awhile. He's also not a knight, bank robber, super-hero, army officer, or a man-eating-slug...but he's pretended to be each of those as well.
Anyhow...like I said, hundreds of reasons/ways that it's not molestation. COULD it be molestation? Yes. Unlikely. Could it be that one of her friends is being molested? More likely (purely a numbers game), but still unlikely.