How does ice form?
For grown-ups: the science
When water gets very cold, its tiny bits line up together and turn into ice.
As water cools, the thermal motion of its molecules slows down, and near 0°C at normal air pressure, liquid water and solid ice switch back and forth. In ice, water molecules link up in an orderly crystal structure through hydrogen bonds. But water doesn't always freeze right away below 0°C - it can become supercooled - so cooling below 0°C doesn't always mean it freezes immediately.
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Transcript
Water turns into hard, solid ice - how does that happen?
Water is made of tiny bits of water, too small to see. When it's warm, they all move around happily.
When it gets cold, the water bits slow down bit by bit. Once it cools below 0°C, they start linking up in neat rows.
The water bits line up neatly and can hardly move anymore. That's how water turns into hard, solid ice.
When water gets cold and can't move much anymore, it turns into ice.