I put mustard on my baby sister at lunch time
What did she do that makes you think she deserves getting mustard put on her?
Well, she's always so annoying, so, I think that she does deserve it to teach her a lesson.
I think that you need to clean her up! It is not okay to put mustard on someone, especially when they are so small.
You need to lighten up. Life is full of surprises, and if she can't handle this, she has no place in the real world.
Kids don't need to get food put on them to teach them lessons about the world. This only teaches them that you act immature and cruel sometimes. Find another way to get your point across.