This prank is guaranteed Halloween fun. Blindfold your child and bring out an assortment of different "body parts" that she has to guess what they are. Use spaghetti for brains, add grapes for eyeballs, bags of pudding for hearts, and slivered almonds for witch's fingernails. Keep her guessing until she gets it right; you'll both laugh at her responses.
Scare up some grub -- and your kid -- with two eggs over-easy and bacon in the shape of a skull and cross bones. Add slices of red pepper for eyes, teeth, and nose.
Use colorful, patterned poster board or wrapping paper to make a life-sized monster -- how scary is up to you -- and hang it in a place your child will least expect for a startling surprise.
Slip in a pair of plastic fangs and ask your child to give you a big sweet kiss. For older kids, use a set of glow-in-the-dark teeth for an illuminating goodnight smooch.
At dinnertime have your kids set the table as usual, then sneak back in to the dining room and put out an extra place setting for a plastic skeleton. Sit the skeleton in the chair; if he can't sit up tie him to the chair with twine or ribbon. Don't worry if it doesn't look artful, it's supposed to be creepy. When your child comes to the table he'll be spooked by the ghastly guest.
Tell your child that you want her to practice polite trick-or-treating. Use a small cardboard box or even an old Tupperware bowl you don't mind sacrificing for this prank. Cut a hole in the box or bowl that's just big enough for you to put your hand through. Tape a piece of tissue over the hole and fill with candy. When your child is ready to practice, hold the bowl with one hand and as she reaches in pop your hand through the tissue-covered hole and give her a good tickle and giggle.
After your child has gone to bed, affix a Talking Tree Decoration ($35) to a tree your child will pass by in the morning. The Talking Tree is motion activated so when she walks by it will blurt out one of its programmed catch phrases, such as "Hey you, come over here!" or "Haven't you seen a talking tree before?" The result: She'll have a fright that she realizes is a lot of fun.
Hit a Halloween store for some not-too-gory temporary scar stickers, such as a simple strip of stitches or Frankenstein bolts. Put them on a noticeable place on your body, like your forehead or elbow. When your child notices your new "scar" pretend to act like you don't know what he is talking about. When the joke has worn thin, let him peel them off you.
Add plastic spiders, ants, or other crawly insects into your ice cube tray. Fill with water and freeze. When your child ask for a drink at dinner, plop a few in his ice water and try not to laugh to hard when he sips... and screams. (Save this prank for school age kids, to avoid any choking concerns when the cubes melt.)
Surprise your child at school by hard boiling two eggs. Make holes in the center of each egg large enough to fit a pimento-filled-olive. Slide the olive in the hole and pack the eggs in plastic container that fits snuggly to prevent the eggs from rolling in her lunch box. When she opens her lunch she will have the eerie feeling that someone is watching her.