When ideas are offered as gifts

I don't know why I didn't think of asking you this before. It's a question that has really bothered me but . . . sometimes the brain overlooks the obvious.  It is a question that has to do with talking about your writing as it is a work in progress, and having other people, either in person or on line, offer you suggestions and ideas which feel perfect.

Then when you use the idea and flesh it out in your story, do you really own it?

Anyway, while my two boys were in grade school, playing youth sport soccer we'd spend a lot of time at the park and to pass the time with the one who wasn't practicing at that time, I'd tell stories and they'd add challenging ideas and a few years later they had developed into my first NaNoWriMo Novel which I published through createspace and kindle. 

But in one of those soccer side, story sessions one of their friends was there listening, and got really into it, and told me to use a character he made up. She was perfect and fit so well and I drilled him on wether he had seen her in a game or book or movie and he swore he made her up just then. Well it was five years later when I took his basic framework and used her as a minor character, but her name was perfect and she seemed so well imagined, I was always afraid he'd stollen her from somewhere. So has anyone heard of

Miskva, Guardian of the singing trees of belle island, who is a seer of prophecy and riddles in a giant but broken pyramid that came into the world as it was being created.

Any manga creation or TV show come to mind, a game or movie or comic book? I'm pretty sure it's a case of can't be too similar the way I created her story from the bare outline above but still I'm curious.  I even had people run her through plagiarism testers and they came back clean, that it hadn't been used in any book - which of course shows how many people have read Duffy Barkley is Not a Dog, because she was used in both my Duffy Books and they are out there.

 I'm remembering this kid was into Star Wars but wasn't allowed to read Tolkien due to parent's religion and ideas about wizards being evil. He loved some card collecting game but it wasn't Pokemon because that also was taboo. He was home schooled so the kids only knew him through soccer and we've lost touch or I'd ask him again

You know I sometimes feel a twinge of guilt using ideas from the NaNoWriMo Website challenge thread too, like it is somehow wrong even though those challenges are put up with the intent that people would use them, but I've incorporated a baby dragon who gets sick in water and loves baths and is named Fred. That was on the nano site forums dare thread, telling anyone who thought they could, to incorporate him into the story, but I don't even know who suggested it, to thank them in my notes.