Sweet dreams I bestow.
Sleep tight, all night.
Forever I will glow.
I decided to add this section, because lot of people seem to think that Joyce's Nightlight is actually Jack, but the first fact that it's not is that the first idea of Joyce's Jack Frost was of an adult that helps the change between seasons. But that doesn't mean that there are no correlations between the characters: the movie Jack Frost and the book Nightlight.
We first meet Nightlight with the Man in the Moon, he is the MiMbaby's bodyguard, and guards him always, because this immortal boy never sleeps. And he is the one that imprisons Pitch Black for centuries, and is imprisoned with him, till the curious moonbeam sets him free, unfortunately it sets free the Bogeyman too.
Even if he doesn't remember much from the past, like Jack, he reacts to it differently, he is happy and likes to play and have fun; Jack also loves to play and have fun, but for him what is mostly difficult it's the fact that he doesn't have a purpose; on the other site Nightlight doesn't seem to have this problem, there are two things he wants to do: have fun and if the nightmares and Pitch appear - then battle them.
But it changes, he meets Katherine, and the fact is she is a child, but she is growing up; he begins getting confused, because before, it was everything simple, there is evil battle it, you have nothing to do? have fun. But with her growing up, also he begun growing up, he was changing, finding new purposes in his life.
So there are the parallels when you look at the appearance of both; two boys, even the haircut almost looks the same, Jack has his staff and Nightlight his spear.
Both of them grow up during the story, and find purposes of their lives, and battle the evil and go on. Nightlight has Katherine, with whom he shares a really deep bond of friendship (they are too young for anything else then friendship love); Jack finds Jamie and Baby Tooth.
The point is, if Nightlight was Jack, where all that growing up would go? Aside, we know Jack's story, he was human before he became spirit.