Sprinkle flour on the floor in the main hallway and nursery. See if it has any physical...well, footprint.

Also, get some sea salt. Most lore suggests salt can negatively affect ghosts and various other spirits. A layer of salt (sea-salt seems to work best) lining any entrances to, say, the baby's room - door and windows - creates a supernatural barrier!

Plus the old Handful-of-Salt-in-the-Eye, gets 'em every time!