Final answer:
A seizure is characterized by convulsive activity, which includes violent muscle contractions, and is caused by abnormal electrical activity in the brain.
Step-by-step explanation:
The nurse would be correct in telling the parent that convulsive activity occurs during a seizure. Unlike a breath-holding spell, which is a reflex response to a child holding their breath, a seizure is caused by abnormal electrical activity in the brain. This abnormal activity can cause violent muscle contractions and loss of consciousness.