Transform your used milk bottles into ghosts and add electric tea candles/ glow sticks to light them up. If the candle is too large to fit in, cut a hole at the back. You can add stones to weight them down or use th indoor with fairy lights instead of electric candles.
This is a very easy project for kids. If they are too little you could make the shapes for them to fill in. We used an acrylic pen and used a spray on top to resist the rain.