One of the projects that I did with my daughter during the last week was to make these little ghosts:
Please excuse the dust on the shelve.
Those guys are made out of plaster of paris. I really enjoyed making them. It does become kinda addictive. I still have some plaster left ... I am toying with the idea of making a mobile or something ...
The only downside of this project is as you are modelling the ghosts on your finger for a bit you are left with only one hand. Really not a good project to do while being in charge of a busy and active baby ... ;-)
If you want to try making them yourself - or save the idea for next Halloween - you can find the tutorial on Art Mind.