The sound of your voice can be very soothing, especially if you are reading words that your child associates with sleep and relaxation. The book, The Rabbit Who Wants To Fall Asleep: A New Way Of Getting Children To Sleep by Carl-Johan Forssen Ehrlin, is designed for this purpose, it uses words associated with sleep and feeling sleepy, to help your child to relax. It is designed to be read while your child is lying down.
One drawback is that your child is likely to fall asleep before the end of the book (that is the idea), and may therefore cry out upon waking at night when you are no longer there, especially is separation anxiety is an issue. However, the relaxation techniques built into the story may also help your child to fall back to sleep independently at night, and you could suggest a couple of the techniques from the book each time your child wakes.
Please add your experiences with this approach in the comments below. Please provide the age of your child when you tried it, and how long you tried it for. If it helped, please share the effects you saw. If it didn’t help, why do you think it didn’t work in your case?