Prince George and Princess Charlotte returned to London with Prince William and Kate Middleton this week.

The royal siblings celebrated the holidays with the royal family in Sandringham, and they also spent time with their mom’s side of the family in Berkshire. But Prince George and Princess Charlotte returned home and are expected to go back to school on Tuesday.

Prince George is studying at Thomas’s Battersea, a preparatory school in London. The third in line the throne started attending the institution in 2017. At that time, Prince George posed for his first day of school photo with his dad Prince William.

Princess Charlotte, on the other hand, is studying at Willcocks Nursery School in Kensington. The 3-year-old started going to the nursery last year.

The royal siblings were last seen in public in December 2018 on their way to Buckingham Palace for the Christmas lunch hosted by Queen Elizabeth II. Prince George and Princess Charlotte joined their parents in their car, and their younger brother, Prince Louis, was believed to have been with them as well.

In related news, Prince George, Princess Charlotte, and Prince Louis’ dad will complete his first engagement of 2019 on Wednesday, Jan. 9, which also happens to be Middleton’s 37th birthday.

Prince William will visit the London Air Ambulance at the Royal Hospital London to mark the facility’s 30th anniversary. Prince William, who previously served as an air ambulance pilot, will recognize the work that their first responders carry out delivering life-saving treatment across London.

During his visit, the Duke of Cambridge will meet pilots, clinicians and paramedics. He will also hear about their and the challenges they face while working in London.

It is still unclear what Prince William has planned for his wife’s birthday. But whatever it is will mostly take place behind closed doors. Last year, the Duchess of Cambridge also celebrated her 36th birthday privately. At the time, she was still pregnant with Prince Louis.

Middleton’s upcoming birthday will also be her first special day as a mother of three so she’s expected to also celebrate the day with her children.