I feel bad saying that your misfortune brought a smile to my face because it brought back fun memories.  When I was about 6 I discovered that the painted wooden PlaySkool people made great colored pencils if you rubbed them on the wall....I drew all over my bedroom wall behind my bed (where my Mom wouldn't see them easily).  There were no magic erasers back then...the whole wall had to be repainted when my Mom finally discovered it!

My husband who has Crohn's says his gut basically acted like a biofeedback machine...he learned not to get upset, because it hurt too much when he did.  Well, I still get upset, but over time I think I have mellowed some.  It is really hard to not let things get to you, and your fuse can be particularly short when you're not feeling well.  

You did one of the best things you could by just walking away from it, since it certainly wasn't time-critical.  Maybe you could sit the kids down (depending on age - probably not the 3 year old) and explain to them that you can't do everything you normally do and as part of the family, you're expecting/relying on them to help out.  Explain just how they can help, starting with cleaning up when you ask them to (if not before!).  You might be surprised how well they take to some extra responsibility.  

Just keep trying to remind yourself that very little in life is improved by adding anger, anxiety or sorrow.  And you'll have a great story to tease your 3 year old with once they're older.  (Too bad you didn't take a picture of the "artwork" for posterity.)