First of all, have you found the pens in your daughter's bag or room or locker? Do you have any way of checking that she might actually have them? She may well not have done, but in case she has read on ...
I was going to change my name for this but tbh I can't be bothered. If anyone knows me, your discretion would be greatly appreciated!
I used to take other people's things when I was small. I was quite a prolific thief - a pencil sharpener from a shop, some toy petrol pumps from my cousin, a necklace from a girl who's house I'd been to, some smurfs and toy makeup from another friend, a Sindy dress and lots and lots of other bits and pieces. It happened over about 2 years, from about age 7-9.
I'm not exactly sure why I did it, but I know I liked the secrecy and thrill of it. I enjoyed the cloak and dagger of the theft bit, and the buzz of almost being caught. I also remember that everyone used to say what a "good little girl" I was, and wanting to do something "bad" instead.
When my mum found out, which she did on several occasions, I swore blind I hadn't done it. I thought that if I denied it enough I wouldn't really have done it, if that makes sense. I was quite convincing, but with some of the earlier stuff I told my mum that it got in my pocket "by magic" and I really couldn't understand why she didn't believe me. It seemed a perfectly plausible explanation to me. My mum quietly gave things back to their owners and the ones she couldn't give back she threw away, so I didn't benefit long term, and it was a long time before she made me face the consequences of what I'd done.
The last thing I took was the Sindy dress. When my mum found it she made me give it back personally, face to face, and explain that it had somehow got mixed up with my Sindy things and that I was very sorry. I was mortified, mainly because I didn't like the girl who it belonged to so I didn't want to apologise. I can't honestly say if it was the face to face thing that stopped me, but I certainly didn't take other children's things again. I do think that if my mum had been tougher earlier I might have been scared out of doing it as I remember being really chuffed that I was getting away with it.
Sorry this is so long, but if it does turn out that your daughter has taken these pens, or if anyone else is in a similar situation, I HTH.