There isn’t any universal theory as to whether or not the metronome is capable of inducing sleep in both children and adults. In fact, it appears that the reason why this device might have such an effect is that it allows one’s body to relax, much like the process of meditation.
However, something that we do feel compelled to note is that, should you want to use a metronome for better sleep or dealing with your insomnia, you’d have to set its rhythm so that it is more or less slow. Practice your breathing and try to focus on the sound instead of allowing your thoughts to get the better of you.