The group has Muslim and non-Muslim members from seven countries including Canada, France and the United States.
In an open letter posted on social media websites, members of Mothers for Life called on their sons and daughters to recall that Islam requires them to honour their parents and spare them suffering.
"Even if you think death will give you that 'better' life, remember that even the Prophet Muhammad (peace and blessings be upon him) said: 'Paradise lies at the feet of your mother,'" the group said. "By leaving us against our will to give up your own life and take those of others, you have put our struggle, pain and honour under your feet and walked over it."
Thousands of young Western men and women have joined the Islamic State group in recent years after being recruited by other extremists, often operating online.
Mothers for Life said their decision to launch the appeal on social media is part of a conscious effort to publicly challenge those who have lured their children away.
"Social media right now seems to be their strength in recruiting our youth," said Canadian mother Chris Boudreau, whose 22-year-old son Damian Clairmont was killed in Syria last year. "We've got to fight fire with fire," she told The Associated Press in a telephone interview.
Boudreau has said her son was actively recruited by individuals in Calgary. He converted to Islam as a teen and reportedly died in heavy fighting in the city of Aleppo last winter as a member of the militant group Islamic State.
The group also wants to help other families struggling to bring their children home, and highlight the need for politicians and security officials to take the parents of foreign fighters seriously.
Mothers for Life is run by the German Institute on Radicalization and De-radicalization Studies (GIRDS) in Berlin. It has several Muslims among its dozen members and also sought advice from Islamic scholars to challenge the religious arguments put forward by extremists.
Mothers for Life website: http://www.girds.org/projects/mothers-for-life-network
Mothers for Life on Facebook: http://www.facebook.com/mothersandlife
With Files from The Canadian Press