Okay kiddo, let me explain it to you. Remember how last year we celebrated New Year's in January, and we will do it again this year? Well, a long time ago, people used a different calendar to count the days and months. This is called the Julian Calendar. But in the 16th century, a new calendar was introduced, called the Gregorian Calendar.
Some people decided to stick to the Julian Calendar, even though most countries switched over to the new calendar. These people are called Old Calendarists. They believe that the Julian Calendar is more accurate and following it helps them stay true to their faith.
These Old Calendarists have a different way of celebrating important religious events, like Christmas and Easter. They celebrate them on different days than most people. They also have different customs and traditions that are specific to their Old Calendarist beliefs.
It's important to remember that different people have different beliefs and ways of doing things. So it's okay if some people celebrate things differently than we do. We should respect their beliefs and traditions, just like we hope they will respect ours.