Why do we have seasons? Many people think that summer comes when the Earth is closer to the Sun. That sounds logical, but it is not correct. In fact, the Earth is a little closer to the Sun in January, during our winter!
The real reason is that the Earth is tilted. Imagine a line going through the Earth from the North Pole to the South Pole. This line is not straight up and down. It leans to one side.
The Earth moves around the Sun once a year. the United States is in the northern half of the Earth. For part of the year, this half leans towards the Sun. The sunlight hits it more directly, and the days are longer. That is our summer. Six months later, the northern half leans away from the Sun. The days are shorter, and the sunlight is weaker. That is our winter.
This is also why the seasons are opposite in the southern half of the Earth. When it is summer in the United States, it is winter in Australia. Some Australian families eat their holiday meals on the beach in December!