Thomson Reuters Foundation

In a sign of the times, US children's show Sesame Street has a new resident: seven-year-old Lily, a homeless, pink puppet.

The newest member, Lily, joins yellow Big Bird and duo Bert and Ernie to offer hope to the growing number of children worldwide who lack a permanent home, said the Sesame Workshop, the non-profit organisation behind Sesame Street.

Homelessness Sesame Street

PICTURE: Homelessness on Sesame Street. PICTURE: Richard Termine/Sesame Workshop.

In 2011, Lily made a brief appearance on the Emmy award-winning show - at that time her family struggled with hunger - and the organisation said the downward spiral from poverty to homelessness was a common path.

"We know children experiencing homelessness are often caught up in a devastating cycle of trauma - the lack of affordable housing, poverty, domestic violence," Sherrie Westin of the Sesame Workshop said in a statement.

"We want to help disrupt that cycle by comforting children, empowering them, and giving them hope for the future."

Although there are no exact numbers for young homeless, globally, at least 150 million people, or about two per cent of the population, are homeless, according to UN-Habitat.

Experts say it leaves young people especially vulnerable to sex trafficking and arrest. With the majority of the world's population now living in cities, homelessness is also growing more prevalent in poor and rich countries alike.

On Thursday, official data showed the number of homeless children living in temporary accommodation in England had risen by almost 3,000 people in the last year - the highest figure in 11 years.

"The fact that more than 123,000 children in England will be forced to wake up homeless this Christmas is a tragedy," said Greg Beales of British homelessness charity, Shelter.

"This is now a national emergency."

Lily and her family will stay with friends on the iconic street after losing their home, and her plight will be used online and in printed materials to help professionals support homeless children.

Her introduction sparked debate on social media with fans alarmed that Oscar the Grouch, a green Muppet who lives in a trash can and hates rainbows and chocolate, had been overlooked as a pioneering homeless star of the 49-year-old show.

Earlier this month, the charitable foundation behind toy maker Lego granted $US100 million to the Sesame Workshop to help children affected by the Rohingya and Syrian refugee crises.