How do I get over the fear of my kids getting a fever after my son had his first febrile siezure?

Difficult problem. Everybody has a different sensitivity when dealing with such a scary event. You feel so helpless. Take comfort in the low recurrence risk even with fever(which will happen) of < 50% & the fact that these events don't damage the brain. Discuss what to do if it does happen with your dr & have a plan in place to deal with it.