Hi there and welcome to HealingWell,
I want to try and clear up a few of your questions, ask a few of my own and also give you some advice (All in one post! lol) Please bear in mind that there are always exceptions to the rule but what I say generally goes for 95% of seizures and that my advice is not a substitute for medical advice from a doctor.
The difference between petit mal and grand mal is an easy one. Petit Mal are seizures where the person seems to lose their connection to the world but does not (generally) fall to the floor. They often stand staring at a particular point and are unresponsive. Grand Mal is what people stereo-typically think of as Epilepsy. Grand Mal seizures often involve the person losing muscular control, they fall to the floor and shake. The term generalised means that it affects the whole brain (and therefore the whole body). The alternative is localised which is where a particular area of the brain is affected (and therefore not the whole body is affected)
The mess up with the Keppra, I agree probably caused the seizure. It seems backwards that an anti-epileptic (AED) can cause a seizure but when you mess up the dosage, it can happen.
How can you help your son and your other children? This is something that I think can be helped by not making this a mountain of a problem. Including your children in what to do when your son has a seizure is a good way of making it seem more normal. Depending on how old your other children are, perhaps a little home first aid training? (Im not talking artificial resus here... just how to deal with seizures!) As for your son, he is highly unlikely to remember the seizure itself since the brain does not function properly and he is unconcious. Does he get (what we call) an aura? This is a feeling or sensation just prior to the seizure. It can be a smell, a sound, a feeling or something visual. I dont have aura's but my mum smells burning almonds. If he has an aura, he may have time to put himself somewhere safe.
The best thing you can do for your son is to research epilepsy and learn about it together. There are many websites in the resource section of our website which you may find helpful. The main thing is not to make epilepsy seem like a huge thing. Although epilepsy generally stays with you for life, you can get periods of remission (which can last decades). So although it looks scary at the moment, there is still hope. I am assuming you live in the US so I cant advise you on driving restrictions, but epilepsy does not stop you driving. You have to complete a set period without a seizure and this is different across states. In the UK it is 1 year and I get the impression that this is a long time compared to the states.
If you have ANY questions, please feel free to ask. There is no such thing as a stupid question if you dont know the answer. Dont let epilepsy control your son... Allow it to be something that he can control.
Best Wishes
Darren