I think you're right, Thelma. There is no reason to explain PD to children who have no need to deal with the illness. It is adults who need to understand our plight.
In BrainTalk there is a sad post about the subject, titled 'Need advice'. TtoyL has posted a really good answer, as has Lindylanka. My answer is exactly in agreement with Thelma's views on this:

"Hello Shawn, I'm very sorry that you have PD at so young an age, and I'm sorry your little girl has to deal with a little too much truth a little too early. Like ToyL I think I have had PD most of my life, and I am very grateful that no one ever noticed the signs, and that I had no idea that there could be another reason for my rigidity and clumsiness other than that I was just a born klutz. I lived for years without knowing the unpleasant and frightening truth.
Many facts and perfect truths are better left unsaid. When you explain PD to a child you must leave out the scary parts.There is no need for your children to know more than that your arm(s) and leg(s) keep forgetting how to do what your brain tells them to do. The telephone lines are crossed and down, and your messages are not going through from brain to body.
Your wife panicked, and confided in the wrong person - had she taken time to digest the news that her husband has PD, she would probably have thought better of it, and not blurted out her own concerns to a child..........."