They probably aren't aware of it yet, but Prince George, 8, Princess Charlotte, 6, and Prince Louis, 3, are the royals of the future. One day George will sit on the throne and rule as king. And big things are in store for his siblings, too.

George, Charlotte and Louis: Royal life and ages

By their 21st birthdays at the latest, the three children of Prince William and Duchess Kate will take on their first royal duties. This is regulated by a law established in 1937 by the Regency Act.

At the age of 21, George, Charlotte, and Louis become Counsellors of State. They step in when the ruling monarch is abroad, for example, or is unable to carry out duties due to illness.

The monarch's spouse and the first four in the British line of succession are automatically Counsellors of State. But there are also a few other conditions...

Prince William, Duchess Kate, Prince George, Princess Charlotte and Prince Louis

To become a Counsellor of State, one must be at least 21 years old, a citizen of the UK, and a resident of the UK.

For Prince George, the time will come by July 22, 2034, when he celebrates his 21st birthday. Princess Charlotte turns 21 on May 2, 2036, and Prince Louis follows on April 23, 2039.

So, things should begin to change for the Cambridge kids over the next decade-plus. George also becomes the Prince of Wales when his father becomes king. It's also possible that, as high-ranking royals, Charlotte and Louis will receive new titles in the future.

George, Charlotte and Louis are still enjoying their childhood 

These days, George, Charlotte, and Louis still enjoy a carefree childhood, and they likely think little about royal duties and offices of the future.

Prince William and Duchess Kate try to let the kids lead a normal life, though reports have said they've begun informing George about his important future.

Like any other child, the young royals also have their first days of school, play sports, and even misbehave a little now and then.