epilepsy in children.. and how can i deal with it whille babysitting?

I baby-sit a 10 year old girl who has epilepsy. I have visited alot of sites on Epilepsy, seen alot of videos and all that.. But I still don't understand something: When a child is having a seizure why does she or he vomit or wet his or her pants? Any experienced parents who can give me an explanation on why this happens and if their child has epilepsy to let me know a little bit more about it. Thank you!
Michelle