I got brown thing on my underwear

I got brown thing on my underwear  , am still 12 , i still don't have period ;-|

I was in the cinema when i entered the bathroom i saw a brown thing on my underwear , when i went home i changed my underwear  and tried cleaning the brown thing from my vagina with a tissue when they started to go i felt relaxed , before 5 minutes i felt that my under wear is wet  i check it was the brown thing again , so what is it ?? am scared and am afraid about telling my mother but i think i will later (tomorrow) :-D

And thanks :))