Susan Pierre, 15, is staring out her window from her room in the oncology ward of the Montreal Children's Hospital.

It's cold and overcast outside. The lights are off. Her room is quiet, except for the sound of the TV.

Then, in walk two people — a man and a woman each wearing a white lab coat, oversized shoes and a round, red nose.

"If we're allowed to be your backup singers, it would be a great, great, great honour," says Melissa Holland, whose clown persona is called Dr. Fifi.

Susan Pierre, 15, is at the hospital's in-patient section of the hematology and oncology division unit. (CBC)

Maxime Larose, the second clown, goes by Dr. Pédalo. His costume is a red and blue swim cap and a yellow life vest.

The two clowns start to beatbox in unison.

After a few bars, Holland launches into a freestyle rap:

"I'm what's known as a corridor surfer,

Doctors and nurses might think I suffer.

But I don't care. I don't care."

Pierre starts to laugh.

"We can be part of your team?" Larose asks.

"Yes," says Pierre.

"They're cool. They're funny. They know how to make you smile," Pierre tells CBC.

The clowns use improvisational music, like freestyle rap, to make patients at the hospital smile. (CBC)

All morning, the clowns wander the halls of the hospital looking for children who could use some cheer.

"We try to bring as much life as possible into a place where sometimes it's a little sterile," says Larose.

The clowns are part of the Dr. Clown Foundation, a Montreal organization that uses laughter to lift the mood of sick children in hospitals and seniors in long-term care facilities.

"I've been doing this for 20 years. For me it's a vocation," says Holland, who co-founded the organization.

Professional performers

When children have a weak immune system and are in isolation, the clowns perform outside their hospital room windows. (CBC)

Holland created the foundation along with two other clowning enthusiasts and a businesswoman. The first performance took place in 2000 at the CHSLD Paul-Lizotte in Montreal North.

Now, nearly two decades later, Dr. Clown is in hospitals around Montreal and Quebec City. The foundation also runs a special program for seniors called La Belle Visite, which operates in more than 25 seniors' homes across Quebec.

The 30 or so clowns who work for the Dr. Clown Foundation are professional performers. Many of them have studied clowning at the Francine Côté's Clown and Comedy School in Montreal.

Clowning isn't just for children's birthday parties, Holland says. It's a theatrical art form that's been practiced for centuries.

"There would always be a comedic figure who would come in … and help the audience just to take a breath," says Holland.

Watch Dr. Fifi and Dr. Pédalo tour the Montreal Children's Hospital:

Therapeutic clowns use improv and physical comedy to put a smile on the faces of sick children at the Montreal Children's Hospital. 2:04

'It's marvellous'

Annie Robert's son has been at the hospital for 23 days. She says the clowns bring a "joie de vivre" to the children staying at hospital.

"It's marvellous. It gives them a moment … when they don't feel pain," she says.

Her son Mickey will leaving the hospital in a week.

Mickey Robert-Charlebois has been at the hospital for almost a month. His mom Annie Robert, left, says the clowns' visits provide a few minutes where her son doesn't feel pain.

Larose believes the art of clowning is a perfect fit in a children's hospital because it reflects the perseverance and vibrancy the young patients show every day.

"The clown, traditionally in the circus, is always getting beat up — but always gets back up with that smile and just keeps going."