My DH is a paramedic, and he goes out to many, many children that have them. In fact it is the most common call out that he gets for young children. Just make sure that you keep his temp under control and don't try and aggressively cool him (meaning chuck him in a cold shower, as it cools them too quick and can cause more problems)

My DS has had them when he was little, but I was lucky as DH was home and treated him.

They are scary, but very common.

Some info to remember
•1 in 30 children have a febrile convulsion at one time or another, usually between the ages of 6 months and 6 years.
•Nothing can be done to prevent the convulsion from occurring, remain calm and try not to panic.
•Putting a child in a bath (to lower their temperature) during a convulsion is dangerous.
•Febrile convulsions will not cause brain damage. Even very long convulsions lasting an hour or more almost never cause harm.
•If the convulsion lasts more than 5 minutes call an ambulance, otherwise make an appointment with your family doctor.
•If you are worried for any other reason, please see your family doctor.