Iantha......dry ice in a container.
If you are careful to keep children from having access to it, you can use dry ice for fog.
Dry ice in a bowl of water. They also have fog machines you can either rent or buy.
I use a fog machine. It's awesome.
I always used to use dry ice. Be careful the stuff can burn you so wear gloves. Found it best to put under a chair or coffee table to keep people from touching it.
You can buy a fog machine at the Party store.