neice says my child touched her

My kids and my sisters kids spent a couple of weeks together at my parents house during the summer.  When my sister was unpacking her 6 year old daughters clothes she found some underwear that had blood on in them.  My niece told my sister that it was my 8 year old daughter who "touched her".  

I've talked to my daughter extensively and I can say with absolute certainty that it was not my daughter who touched her.   There is no family history of sexual abuse with our parents and we are very confident that it wasn't our parents who touched my niece.  

I am not at all denying the fact my niece was touched but I know my child, and I know my daughter is telling the truth.  Do children frequently blame another child when they are abused by someone?  How can we get to the truth of who could be abusing my niece and stop it from ever happening again?

[margypops]

This is an upsetting situation isnt it, your sister should have a talk with her Daughter and ask for the details ,and you could do the same with your daughter, curiosity is pretty widespread and considered to be Normal, However the sound of Blood on underwear is what you would both look to address. Maybe you all 4 could have a group discussion and see what comes out, you should be able to read their Faces and see how they behave when confronted ,who is lying and who is not.