How Kate Middleton’s Kids Are Helping Her amid Cancer: ‘Extraordinary Resilience of Children’ (Exclusive)

kate middleton kids, Prince George, Princess Charlotte and Prince Louis, are a special source of support as she receives cancer treatment.

“You take heart from the extraordinary resilience of children,” a longtime family friend tells PEOPLE exclusively in this week’s cover story.

The Prince and Princess of Wales are getting through her health crisis with support from Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5, who “buoy them with smiles back,” the family friend says.

“Having fun together when they can is very important,” the insider adds.

“The children are at the center of their world,” the friend adds about Prince William, 41, and Princess Kate, 42, which was made clear in the royal’s cancer announcement and the timing of it. The Princess of Wales waited to make the public announcement about her health until after her children were out of school for the Easter holiday. George, Charlotte and Louis aren’t due back in the classroom until later in April, creating space for the family to spend private time together.

“We now understand the logic of the timing — waiting for the children to break up from school. And she struck a pitch-perfect note,” royal biographer Sally Bedell Smith tells PEOPLE about Princess Kate’s video message, which sent shockwaves around the world on March 22.

The Prince and Princess of Wales’ family subsequently skipped the royal family’s church outing on Easter, breaking tradition from past years.