The mother and father of murdered Queensland boy Daniel Morcombe also attended the launch in the national capital of International Missing Children's Day, pleading with estranged parents to never take the option of abducting their child.

Bruce and Denise Morcombe were at the launch to show support for the families of the missing children, with both saying no parent should ever abduct their own child, saying there was help if people were in distress.

Their own son was abducted and killed by a stranger, in 2003, but his remains were not found until 2011. The Morcombes said a parent should never inflict that same agony of a missing child on their own partner and wider family.

"It's a very selfish decision that they're perhaps contemplating and please don't go there," Mr Morcombe said.

"Help is available and what they really need to focus on is that their love for the child is misguided. It takes two to bring a child into the world. And leave any decisions to the authorities.

"It's really important that the child comes first. Not the mother or the father."

The Australian Federal Police used International Missing Children's Day to highlight the cases of six children missing for years but still aged under 18. The theme of the day this year is around the use of aged-progressed photographs.

Leading forensic artists from the United States National Centre for Missing and Exploited Children were commissioned to create the age-progressed images to illustrate what the children may look like today.

Sydney father Michael Macintosh has not see his son Mathieu-Pierre since September, 2013 when the then nine-year-old left home for what was meant to be a six-week holiday with his mother in France.

Mathieu-Pierre is believed to be living in France or Belgium and is subject of an order issued by the French courts under the Hague Convention to have him returned to Australia.

Mr Macintosh gave an emotional speech to the launch at the National Portrait Gallery, referring to a UK study that found most abducted children suffered mental anguish akin to being sexually or physically abused.

He also remembered all the little details about his son, including his love for Bob the Builder as a toddler.

In a direct message to his missing son, now aged 13, Mr Macintosh said: "I will keep looking until I find you. We can fix it. Yes, we can. I love you, dear Matt".

The emcee for the event, retired member of The Wiggles and former early childhood teacher, Murray Cook, was close to tears as he thanked the families for being brave enough to share their stories.

Harry Speath wept as he looked at the images of his missing children, Serena and Thomas Speath, who have been missing from Queensland since December, 2014, believed to be with their mother. Serena would now be eight and Thomas, seven.

"They remind you of the time you've missed with them," Mr Speath said.

Michael Watter had sole custody of his non-identical twin girls, Bronte and Isabella Watter, when they were abducted from their Townsville primary school, allegedly by their mother, Cassie Watter, in 2014. A warrant for her arrest has been issued. The girls would now be 10.

"They've been gone a long time, they've changed a lot in those three years. And I've missed a lot of time with them," Mr Watter said.

AFP Assistant Commissioner Debbie Platz, national manager crime operations, said it was hoped the images would spark interest in the children's cases and ignite a global effort to bring them home.

About 38,000 people were reported missing in Australia each year and of those, about 20,000 were aged under 18.

"Most of them are actually found within the first couple of days so that consists of children who might run away or fail to tell their parents where they are or they're abducted by one of the parents and then they're located quite quickly," she said.

The AFP received 400 recovery orders each year from the Family Court for children missing with, or abducted by, a parent. On average, there were 141 applications to have children returned to Australia via the Hague Convention after being abducted overseas by a parent.

Assistant Commissioner Platz said there were genuine cases of parents fleeing situations of domestic violence but abducting children and breaking the law was not the answer.

"I've seen that when children are returned, as they get older, they will often turn on the parent who has abducted them. That parent will then lose contact with that child themselves," she said.

"So you're causing them trauma all through their life."

Victorian couple Jim and Cathy McDougall, both in their 60s, were also at Thursday's launch. Their daughter Chantelle and grand-daughter, Leela,went missing from Western Australia in 2007 with two men, including Leela's father. Leela would now be aged 15.

The McDougalls have spent the past decade searching for their missing daughter and grand-daughter.

"You just have to cope. Every day you think of them. You just have to take one day at a time," Mr McDougall said.

"We just really want to know they're okay. The not knowing is the hard bit."

Mr Macintosh, meanwhile, said with the help of the police and tools such as social media, he looked forward to a reunion with his son.

"I'm actually very hopeful that I'll find him. I think it's just a matter of time," he said.

"In this day and age, there's a lot of technology that can help. You can't run forever."