julie
My daughter had one febrile seizure when she was just 2 years old so I know how frightful they can be. What I learned was that it isn't a case of having a high temperature that triggers a febrile seisure; it is a case of a quickly escalating temperature. That rapid temperature spike sends a message to the brain to "shut off". So, it appears that your son's temperature spikes quickly in the lower ranges. I would probably investigate fever management strategies that regulate his temperature. Also, Ibuprofin for children (ex. Advil for kids) worked very well to keep my daughter's fever controlled. Good Luck!