"How's the baby doing? Sleeping through the night yet?"

This line will be familiar to parents of small children. The unbroken, "normal" night's sleep is the holy grail of parenting. Gwyneth Paltrow's daughter might have started sleeping through the night from six weeks, but for most families that's a distant dream.

It's perhaps the most talked-about topic on online forums, and there's an entire publishing industry based on the idea that with the right training, babies can and should sleep more.

Here, BuzzFeed News speaks to two leading experts to find out why babies wake up during the night – and why it might actually be a good thing.