Frankly, I had heard long ago that phenobarbital can cause a decrease in IQ...
I just googled it, and found this abstract (short summary) of research done on that... granted, it was done in published in 1990 (New England Journal of Medicine), but they were using it for febrile seizures, also...
http://www.nejm.org/doi/full/10.1056/NEJM199002083220604
I would really question whether it is worth the risk, although I do understand what the neurologist is saying, that since they are becoming such long seizures, there is risk of permanent damage, also.
btw... I have epilepsy, and have had 2 grand mal seizures. I've been seizure free for over 13 years, though. I'm not currently on medication. They felt the seizures (in my case) were caused in part to some medication I was taking. I couldn't tolerate Dilantin, and used Tegretol very successfully.