If your young children are anything like mine, they have a "Favourite" torch that they like to keep near their bed for toilet runs or just a comforter. These 3V, AA battery burners consume a pair of batteries every night on the incandescent bulbs supplied.
You can easily and cheaply replace that annoying bulb, with an efficient white LED with no soldering required!
A quick tip about LED's and polarity. They will only let the current flow in one direction. If you reverse the leads, which aren't really obviously marked, then it will not illuminate and in some cases may burn out. The way I remember how to pop them in a circuit.....
The shorter lead (Cut) is the Cathode, which goes to Negaive, or Ground.
It's also got the fatter lump of metal inside the epoxy if your leads are the same length.
Step 1: Preparation
First, pull the torch apart. Most kid torches have a small screw holding the bulb section on to stop them from eating the bits (apparently). Disassemble the entire lense and reflector. Find a nice small plastic stand-off. I have quite a few of these motherboard supports from back in the Pentium III days, and they fit insid the bulb hole perfectly.
Step 2: Preparing the "Bulb"
Cut any excess bits off the plastic that you don't need then drill two small holes in the plastic housing. One pretty much centre, the other off to the side.
The centre pin will be the Positive (+) pin, which will touch the nub end of the AA battery. Curl it around a bit, as pictured.
Step 3: Finishing Up.
Next, you want to reassemble the new LED bulb into the reflector and lens. Centralize it the best you can, some slight filing might be in order.
Bend the Negative (-) lead out, and in my torch, position it so you get the most surface area on the metal frame cover. This cover also touches the switch to complete the circuit.
Put in two fresh Alkaline batteries, and bask in the new longevity of the modified torch. It should run for several weeks continuously now. The 3V supplied by the two AA batteries have not burned out any of the torches I have modified thus far. White LED's operate from about 2.5v and will let the magic smoke out above 4.2V, so 3V is about perfect.