Campaigners have welcomed a new bid to help some of the 140,000 British children whose dads will spend Father's Day behind bars.
Action for Prisoners' Families (APF) said a new booklet produced by a crime-reduction charity would help prevent children suffering because of their parents' behaviour.
Nacro's Outside Help publication gives practical advice about how the prison system works, contacting and visiting procedures and coping financially.
APF director Lucy Gampell said: "This Sunday will be a poignant reminder of their dad's absence for thousands of children of imprisoned fathers. They are living with the stigma - or the secret - of having a parent in prison.
"Many become withdrawn, perform badly at school and suffer from mental health problems. Many others do not get to see their dads, who are often imprisoned a long way from home.
"Despite rising prison numbers, visits are declining and nearly half of all prisoners lose contact with their kids and other relatives.
"We hope that Outside Help will reach as many families as possible and help them understand such a confusing and intimidating system, making it easier for parents in prison to stay in contact with their children."
Jackie Worrall, Nacro's director of policy and public affairs, said: "Family breakdown while a prisoner is serving their sentence can contribute to the likelihood of reoffending on release, so it is vital that family ties are maintained.
"The support of family and friends can be crucial in helping a prisoner to work through their sentence successfully.
"Outside Help provides practical information and advice to families who want to support their loved one, but often don't know where to start. The prison system is complex and full of jargon and this booklet aims to break down a lot of that confusion so families on the outside feel less excluded from what is happening on the inside."
