Crisis of conscience

So, if Julia is shoving, yelling at or otherwise acting inappropriately toward her brother, and Evan is giggling gleefully and relishing the attention from his beloved big sister, what's my obligation here? Should I:

A) Break up the scuffle and reprimand Julia for behavior which would horrify me if she directed it at any other child

B) Praise Julia for keeping her little brother entertained

or

C) Pretend not to notice and use the time when no one's bugging me to get stuff done around the house

Does the answer change if I confess that my definition of "get stuff done around the house" typically involves bargain hunting for expensive children's clothing on eBay and writing a blog entry?