Marymead has been providing family support services to children, young people and their families since 1967.

The FranciscanMissionaries of Mary established the service when the sisters saw a need in Canberra for a residential care facility for children and families in temporary crisis.

Sunday marks exactly 50 years since its official opening, on February 26, 1967, on what was then an 11-acre paddock in Narrabundah.

A Family Fun Day is being held at Marymead's Narrabundah site in Goyder St on Sunday, February 26, from 11am to 3pm.

There will be a jumping castle and lots of free activities for the kids, a sausage sizzle and soft drink for gold coin donations, entertainment and more.

Not only its 50th anniversary year, 2017 promises to be a year of change for Marymead.

It has had a development application approved to redevelop the site, building new facilities for its family services including new cottages and using the surplus land to construct an 85-unit retirement village.

The $40 millionredevelopment is set to begin in the second half of this year.

In August, Marymead will move its services off-site for two years while the building work is done. Its counselling and other services will shift temporarily to the Rheinberger Conference Centre in Narrabundah and it will lease two houses for short-term care of children.

Marymead's chief executive officer Camilla Rowland said the services would return to the original Narrabundah site after the build, the centre to be vastly transformed.

"This year is without doubt one of the most significant years of Marymead's long history," Mrs Rowland said.

"While the day will celebrate Marymead's special birthday it also gives those connected to the original Marymead site in Narrabundah an opportunity to farewell the site before the redevelopment commences in the latter half of the year."