In my world, spirits are everywhere. When a child is born, they collect to it, and a select few are chosen to remain with the babe as she grows up, protecting her from harm, helping her with school work, and otherwise nurturing the child unseen. Perhaps she is behind on her homework. They encourage the teacher to take the week off and go on a cruise... giving her more time to finish it. Perhaps they know an accident is coming, so they distract her with a beautiful snail shell, causing her to be reprimanded by her mother for dawdling, but also saving her life, for her mother ends up driving off several minutes too late to be involved in the accident. If they know she will tend to be too full of pride when she is older, they allow bullies to chant an ugly name at her on the playground, so that she can learn what pain feels like and not cause it in others.
These spirits tag along on the roof of the car, their light, wispy clothing blowing in the wind (if she's on the highway, they can create a wind shield for themselves, if they want to talk or to hear what's going on in the car. They follow her to school (though they do tend to detest buses). They dance with her late at night, when she thinks she is alone in a dark living room. They sit on the bed with her, rubbing her back as she cries after a fight with her brother.
As she grows up, they stay with her, humming to her babies as she rocks them to sleep. Their humming lulls her exhausted body to sleep as well, and they hold them both, mother and baby. When she fights with her husband, they soothe everyone, helping the couple come together and talk about it later, when she isn't so angry. When her appendix bursts, they make sure she's close to the hospital and shopping with a friend, so that she survives.
The girl thinks she is alone all her life, but she isn't, and a few times she senses the other side... especially when she gazes at a lit Christmas tree or hears a song on the radio that vaguely reminds her of them. But these stray thoughts rarely turn into an awareness. After all, she thinks, she needs to live in the real world, not a fantasy, and people like these spirits cannot possibly exist.
And when she dies, these spirits are still there, waiting to take her home, excited that, for once, she will be able to see them clearly. Then, perhaps, she will tag along with them on their next adventure, when they help another child enter the world.