I was once given some balloons by the local shop. When I tried to do electrostatics experiments with them they didn't work.
...They were free of charge!
Summary
Charged balloons
Like charges repel and opposite charges attract. A balloon isn't normally charged; you have to rub it. This adds negative charge to the surface of the balloon.
Neutral objects can have a charge induced within them if a charged object comes nearby.
Atomic charge
If matter can be charged and matter is made of atoms, then atoms must contain charge.
Electrons are negative
The nucleus is positive
Some materials contain electrons that are easy to remove, others like to hold onto them.