I was dx'd when my dtr was 8 months old and my son was 2. The easiest way I found to explain it was that mommy's brain is sick, it gets "holes" in it, and stuff I'm supposed to remember just falls out! I also got a children's anatomy book and showed them the brain and nervous system when they were a little older, and explained how the "slippery stuff" that made the nerve messages go fast was missing in places, so they would go slow and have traffic jams.

I've always been very open about any medical issues I'm having, letting them see my surgery incisions or watch me take my shots or whatever. They usually want to know: 1. Are you going to die? and 2. Does it hurt a lot? Once I've reassured them on these points they are pretty well satisfied. And I try to substitute things I can do for things I can't, like I can't play soccer with you, but I'll be your cheerleader from the porch. Kids can be a big help from a very young age, you'd be surprised!