We have plastic covers over all of our stove's knobs. You need to remove the cover before the stove knob can be turned, and it takes enough arm strength to open the cover that this is one of the few safety precautions we've implemented that our children have been unable to beat - so far.
The link is below (assuming LiveJournal's HTML rendering is standard):
stove knob covers
The link is below (assuming LiveJournal's HTML rendering is standard):
stove knob covers (http://www.amazon.com/Safety-1st-Stove-Knob-Covers/dp/B000LEXBYM)