Moisture
Moisture is the small amount of water found on a surface or in the air.
A cold glass of water sits on a wooden counter. Tiny droplets form on the outside of the glass. Water vapor in the air hits the cold glass and turns to liquid. That thin, wet film is moisture.
Explaining moisture by grade level
Put one piece of bread in a dry bag. Put one piece in a damp bag. The damp bread grows mold much faster. Mold needs wet places to grow, so dry bread stays clean longer.
Projects that explore moisture
Moisture is water on a surface. Mold needs that water to grow. You add a few drops of water to bread and seal it in a bag. The water stays on the bread's surface. Within a few days, fuzzy patches of mold appear.
Moisture is the small amount of water on a surface. You add a few drops of water to one bread slice to increase its surface moisture. That damp slice grows mold first because it has the most water on it.