I don't remember when I stumbled upon this, but it's been something of a lifesaver. A couple of years ago I came across a copy of Kipling's 'Just So Stories'. You know, the one about how the camel got its humps and so on. The kids enjoy them, but they have trouble staying awake through them.
The stories are straight-forward but they have certain elements that bring on the drowsy. Kipling has long phrases that he repeats several times. For example, in the wonderful story about the Elephant's Child, he writes about 'the great grey-green greasy Limpopo river all set about with fever trees', again and again. The phrase is wonderful but it has a certain lulling quality.
Anyway, it works. Usually one story will do it. On hard nights (like tonight) I pull out the big guns. I just gave Relia twenty minutes of the wonderful story, 'Kim'. We read about poor orphaned Kim and his meeting with the Tibetan lama. We read about the Lama and his journey to find a holy river. Well, I read it. I think she was out cold by then.
Seriously, try it. Get the unedited, full length version of some Kipling. (It was written more than a hundred years ago, so you may need to do some editing of your own...) But go out and get it. You won't be disappointed.