The following is an exercept from the book "Night parade of one hundred demons" also known in japanese as the Hyakki Yagyo. Detailing the Myth and Lore of the Yokai (Ghost, strange being, beings, etc.)
You can buy a copy of this book at amazon: http://www.amazon.com/The-Night-Parade-Hundred-Demons/dp/0985218401/
Note: Im not on a path involving Shinto so if anyone who does practice it and has anything to add, feel free to do so. Im no authority on the subject
Appearance: Zashiki warashi are house spirits, fond of mischief, loved by all, and believed to bring great fortune and riches to those whose houses it haunts. They appear as ghost-like five or six year old children with blushing red faces. They can be boys or girls, and usually wear tradition clothes; child-sized warrior costumes for boys, patterned kimonos, with short, bobbed, or long, tied back hair for girls. Rarely they appear as wild, hairy brutish figures. Often it is difficult to make out any details other than a vague child-like shape. Direct sightings of these ghosts are rare. In some instances it is said that only the houses owners, or only children, are able to see these spirits. Because of this, they are usually known only by their pranks.
Behavior: Zashiki warashi love mischief. Often the first signs that ones house may be haunted by one is a trail of childrens footprints going through ashes or soap powder. Other mischief includes making phantom noises which sound like spinning wheels turning all night long, paper crinkling, childrens voices, or kaguraShinto holy music. Most hauntings involve a single ghost, while some involve multiple spirits.
Interactions : Zashiki warashi are considered guardian spirits of the house, and gods of luck. It is said that a house with a Zashiki warashi will prosper and grow rich, and a house that drives away such a spirit will fall into decline and ruin. In one account, a family witnessed a zashiki warashi leaving from their home, and soon they all succumbed to food poisoning and died. In another well-known legend from Iwate, a wealthy mans son shot a zashiki warashi with a bow and arrow, and soon after the familys fortunes collapsed.
In many homes, these spirits befriend the children of the house, teaching them songs, games, and nursery rhymes. They keep elderly or infertile couples company, and these couples often treat the zashiki warashi as if it were their own child. The desire to attract and keep these friendly yokai has led to customs like setting food out in the zashiki for them, and even laying coins in the foundation when building a new house. The Japanese take great care to maintain their zashiki, so as not to drive out any guardian spirits dwelling there.
Other Forms: Their common name comes from the zashiki, the formal reception room for guests in a Japanese house where they most often reside. They are known by many different names in other areas, such as kurabokko (warehouse child) and makuragaeshi (pillow turner). Countless variations of zashiki warashi exist from place to place, with minor difference in their appearance and habits.