We have seasons because of the way the Earth moves around the sun and the way the Earth is tilted on its axis.

The Earth moves around the sun in an orbit, which is like a big circle. As the Earth moves, different parts of it get more or less sunlight. And because the Earth is tilted on its axis, different parts of the planet are facing the sun at different times of the year.

When the Earth is tilted towards the sun, the days are longer and the sun's light is stronger, which makes the weather warmer. This is called summer.

When the Earth is tilted away from the sun, the days are shorter and the sun's light is weaker, which makes the weather cooler. This is called winter.

And in between summer and winter, we have spring and fall, which are seasons where the weather is changing from warm to cool, or from cool to warm.

So, the reason we have seasons is because of the way the Earth moves around the sun and the way the Earth is tilted on its axis. This causes different parts of the planet to get more or less sunlight, which changes the weather and creates the different seasons.