K.I.
I kind of do...
When I was a teenager I lived with my cousin and she had 2 small girls...my cousin was (sadly she passed away way a few years back) a diabetic and throughout her life she would have the occasional seizure when her blood sugar was too low. We had to have that conversation with her girls, as a family, when they were a bit younger than that. I remember my cousin was very honest and did her best to explain it. I think the most important thing is to reiterate the fact that the person having the seizure will be OK and to inform them of anything they should know if it happens while they are alone, as well as to be sympathetic about how darn right scary it is for the lil' kids to see and process.
Hope this helps!