Here's a neat way to introduce a measure of security to drawers: The Covert universal lock, a project currently under development consideration at Quirky. It's a simple magnetic latch that you attach to the inside of the drawer. Touching the included magnetic key fob to the front surface of the drawer engages the magnet, allowing you to slide the unseen latch open and closed.
It might not be enough to stymie an observant and theft-minded adult who knows where to buy magnets, but at the very least it oughta keep Junior out of your pills drawer. (Just make sure you attach his drawings to the 'fridge with Scotch tape, not magnets.)