Oh my goodness!!! I can only imagine how you feel!! I live in terror of something like that happening to me - I have a two year old and she is VERY interested in everythiing Mommy does.
Since your cashmerino is washable, I think that is a good sign, but I can't imagine washing an unfinished project - you would have to wash the yarn it was attached to as well, and I think you would just end up with a knottted mess!! My inclination would be depending on how far along you are is to just finish the scarf and then try washing it when you are done, but you run the risk of finishing and having it be ruined. You could try handwashing the stained part in the sink - then you would have control over it the whole time.
Good luck!! Let us know how it comes out!!