I took apart one of those kids shoes that flashes to see what the battery/circuit/sensor looked like. Here it is:

A small coin cell (under the round sticker), a circuit board, and a spring sensor are embedded in a square block of resin. It has three output channels (labeled R,G,B, although in this particular shoe all three were connected to red LED’s).   One LED (shown) was pointing out the back of the sole, and the other two were on top of the shoe. It took me about 5 minutes with a razer knife to dig this out of the sole of the shoe, and another 5 minutes to cut out the wires that went up to the red LED’s on the top of the shoe. Here is a video: