Young niece masterbating

I once dated a kindergarten teacher who told me that this is super normal for young girls. Happened often during nap time. She said it's usually a phase they just get over as they get a bit older. Probably avoid getting involved though.

Things like this can break apart a family very quickly. Even if her parents don't press charges, you would an outcaste from the family. I have seen this over money. Very sad.

I understand that kids can be persuasive but don't give in to her questions.

She is telling you this, since she trusts you totally. Like most kids, they don't want to talk to their parents on a subject so personal. I would just give her sound advice and keep her secret for now.

No, don't watch her and don't help her. Think about her in ten years looking back and knowing that she masturbated in front of you, it's not a bonding moment, that will most likely cause high amounts of awkwardness and confusion. Tell her it's something for her to explore, in private (not while you or anyone else is in the room from now on), to see what feels good. She doesn't need instructions, if it's pleasurable she'll do it. Frankly, I'm surprised that she started at five and still isn't sure if she's doing it right.
If she persists with asking how to then you can explain the anatomy but you should avoid 'probing' or anything like that.

Also, this is your niece, not your responsibility unless you've adopted her. You really should not be watching or helping in any form. The fact that you aren't even mother/daughter means that this exceeds even the barely tolerable levels of interaction. Try not to embarrass her in front of her parents by telling them, just make sure she knows not to do it with other people around. It could be a problem if she does it during school.

One word: DON'T.

She can do this in her alone time and learn about it herself .

SHES TEN YOU SICK BASTARD, why are you exploring this at all? She is, let me say it again.... TEN

She's a little girl. Not even developed yet. Can't believe you would even raise the question. Even on here that's out of place.

No. Say no. Say Fuck No. Back the Fuck Up and Say Oh Hell Naw.

She is jail bait like you wouldn't believe. Because it won't stop there. It'll go on until you find yourself in jail with a dick up your ass and you'll retrace your problem back to here.

Do not help her. Tell her parents if you really need to do something. But you're the uncle...that's creepy.
No.