Okay kiddo, a long time ago, there was a place in the Middle East called Canaan. Later on, a group of people called the Israelites started living there and called it Israel. Then, many years later, the Romans took over the area and they renamed it Syria Palaestina, which means "Philistine Syria". This was to punish the Jews for rebelling against them.
However, the name Palestine didn't really stick until much later in history. After World War I, the area was under the control of the British Empire. They called it the British Mandate for Palestine, which just means they were in charge of it and decided to name it after the ancient name that the Romans had given it.
Then, in 1948, Israel became its own country and the area that used to be called Palestine was split into two parts: one part became Israel and the other part became known as the West Bank and Gaza Strip. To this day, there's still a lot of debate about what to call that area and who it belongs to. Some people call it Palestine, others call it the Palestinian Territories, and other people call it the Occupied Territories.
So, the name Palestine has a long and complicated history, and different people have used it to refer to different things at different times. But it all started with the Romans, and the name has stuck around in different forms ever since.