Triangle, square, circle — the first shapes kids ever meet. But why is a triangle called a "triangle"? The answer is very simple.
A triangle has 3 straight lines, called sides. It also has 3 pointy points, called corners (or vertices). That's why it's a tri-angle. A square has 4 sides and 4 corners.
A "side" is a straight line that makes up part of a shape's outline. A "corner" is the pointy spot where two sides meet. A triangle's 3 sides meet to form 3 corners.
A four-sided shape (square or rectangle) has 4 sides forming 4 corners. A five-sided shape (pentagon) has 5, and a six-sided shape (hexagon) has 6. For these shapes, the number of sides and the number of corners are always the same.
A circle is a little different. It has no straight sides. It has no pointy corners either. It's made of one single curved line that loops all the way around.
That's why a circle is a different kind of shape from a triangle or a square. Ask your child, "why does a circle look so different from a triangle or a square?" and let them find the difference between straight lines and curved lines themselves.
Shapes like these are hiding all around us. Road signs are triangles or circles. Windows and books are rectangles. A honeycomb is made of hexagons.
Take a walk around the house or the neighborhood with your child and ask, "what shape is this?" It helps shapes feel less like pictures in a book and more like familiar things in everyday life.
The best way to practice is to point at each side with a finger and count "one, two, three." It also helps to cut colored paper into triangles and squares and stick a sticker on every corner. Counting the sides and corners with your own hands makes it click why each shape got its name.
On our activity page, choosing a shape shows an animation that counts its sides and corners one by one. You can also try a simple quiz to name the shape. Click through different shapes and discover for yourself that "the more sides a shape has, the closer it looks to a circle."