i explained it in very simple terms to my 8 year old when I had to go to the hospital. The three year old only knows that I sometimes get a boo boo on my brain and I have to go to the doctor to get it fixed. I will sit them down when they are old enough and tell them flat out what it is and what it means for us as a family. My kids actually handle my mood swings better than I do. They are really great.