When I looked underneath his bed, I realized that I had recently placed a powerstrip to connect his aqaurium next to his bed. The blue LED light on the powerstrip was so powerful that it lit up the entire room. I quickly got some black electrical tape and placed it over the light, and the room was dark again. (Duct tape would have worked as well.)
I've noticed over the years that with more efficient LED lights on electronic appliances, our bedrooms can be lit up to the point of preventing a good night's sleep. In our bedroom, I taped off our air purifier (5 different places), our wireless phone (which was really bright), our humidifier, and had to turn upside-down our two cell phones as well. Not only are individual LEDs much more powerful than a standard night light, a typical bedroom can have 3-5 bright lights, which can prevent someone from falling asleep. Even my new alarm clock is MUCH brighter than my old one.
There's been much written about how the invention of the light bulb really disturbed our sleep patterns in this century, and the proliferation of more and more powerful LEDs are definitely taking it up another notch. Lack of light is what signals our brains to produce signals to initiate sleep. Besides all the other distractions that prevent us from getting proper sleep (such as televisions, cell phones, internet, etc.), we don't need more lights.
So take a few minutes and survey your bedroom, as well as your children's bedroom. Make sure you give your eyes a few minutes to adjust to the darkness. Then cover anything that emits light with a small piece of black electrical tape or duct tape.
Another option, of course, is to tape your eyes. But you could get an eye mask instead.