We went down to the pharmacy and bought a pill cutter. We have to cut lots of Jon's tabs anyway, because they come in much larger sizes than are appropriate for a child. For instance, our doc prescribed 250 Keppra in AM and 250 PM, but they come in 500 mg tabs.
Is he able to take the liquid form? The good thing about the liquid is that you can increase and decrease the dose in 50 mg increments - and the syringe that comes with the bottle can hold a dose of 1000 mg. The bad thing about the liquid is perhaps the taste. It can also be hard to get a small child to take it. My son is 14 months old and really hates it. With an older child, though, it might be possible to mix the medication with a juice or food that he likes.