This is promising:
Among children taking cannabidiol, the decrease in the frequency of convulsive seizures — which involve a loss of consciousness, stiffened muscles and jerking movements — was 23 percentage points greater than the decrease in seizures among children taking a placebo. The study was a randomized, double-blind, placebo-controlled human trial.
They were looking specifically at children with Dravet Syndrome, which is described as “a severe childhood-onset epilepsy that causes multiple kinds of seizures, developmental delays, speech and language problems, behavioral issues and movement and balance problems.” Sounds pretty awful. If nearly a quarter of those children respond well to cannabidiol, wow. Especially since other treatments are apparently not super useful for this syndrome.