[Brainchild]

There are a couple of things that cause battery leaks, between heat and corrosion of the terminal plates, so most batteries have a varying lifespan but all will eventually leak as they discharge. Basically, the system will begin to produce Hydrogen gas over time, which is sped up by excess heat. The gas increases the pressure inside the battery, and it triggers a fail-safe pressure seal in most batteries, which ruptures one of the terminals and causes Potassium Hydroxide to leak out of the battery. Between that and a small explosion, leakage is a much nicer option.

The best way to avoid damage to your devices is to check them often. If the batteries discharge, then take them out of the toy and dispose of them immediately. Don't mix different types of batteries, since one's mechanism may need to work faster to maintain the circuit and build up excess heat. Obviously, cheap batteries have thinner shells and can rupture more easily. A good rule of thumb is to just not have batteries in a toy unless you're actively using the electronics.