Welcome to HealingWell.
Bipolar is believed to be genetic. See here: www.nimh.nih.gov/health/publications/bipolar-disorder/complete-index.shtml
I'm not sure what you mean by "protect" your children. From developing the disorder? From someone suffering from this disorder? That's unclear.
Have a look, incidentally, at our "welcome" post: www.healingwell.com/community/default.aspx?f=13&m=883428
No, you cannot tell a 2 year old something is wrong with mommy's brain, but you can reassure your children that ALL people experience moods, and that is okay. Sometimes we're happy, sometimes sad, but no matter what their parent's mood, they are loved. There's no need, at this stage, to go into the whys and wherefores.
SerafenaCo-Moderator, Bipolar and Depression ForumsBipolar II
"Bipolar disorder can be a great teacher. It's a challenge, but it can set you up to be able to do almost anything else in your life." - CARRIE FISHER