I'm really open with DD, as a single mum she sometimes has had to be my tampon fairy and bring them to the loo since being little.
She knows I 'have blood' as she calls it and about periods in general.
I switched to a mooncup a while ago but DD has never encountered it. She came in when I was in the bath, saw it on the side and asked what it was. I said it was instead of a tampon/pad to catch my blood when I'm on my period.
She then asked if I held it under me when I wee'd to catch it. I automatically replied, no, it goes inside me in my vagina and stays there to catch it. She said 'ewwww' and left it there.
Bit worried I explained too far with the inside me part.