Why are there only 4 seasons in a year for kids?

Answer 1

It's because of the way the earth spins on a 'tilt'. For a time, we tilt away from the sun and night time is longer than daytime, and that is winter. Then for a time after winter, the days and nights are roughly the same length, and temperatures go from cooler to warmer as the days get longer, and that is spring. Then we tilt closer to the sun, and day times are longer than night time. That is summer. After summer, the days and nights get closer to the same length again, but temperatures are going from warmer to cooler as the days get shorter. That is fall or autumn.

Unless you live close to the equator, you will notice that the lengths of daytime and night time are always changing little by little.

Answer 2

This is a cultural bias. The Samí of northern Scandinavia have eight seasons. You could divide into as many as you wanted but four is easy to deal with.