Gillian and Neville Howe, from Silkmore Lane, in Stafford, have fostered more than 40 children since starting in 1977.
The couple, who have three children of their own with another adopted, said their key to success was patience and communication.
Neville, aged 76, said: "Without a doubt fostering has been the best thing we’ve ever done in our lives. For me, seeing the children grow up to be kind successful young adults is an amazing feeling.
"Things have certainly changed since we started back in 1977 when the children were pretty much dropped off and you were left to get on with it. Now there’s much more support and training available to help which is really good.
"We are still in touch with some of the children we looked after and it’s always nice to hear how they are getting on. We still get regular calls too from them asking for advice on different things, so that’s nice and we’re always happy to help out.
"Being called ‘mum and dad’ also makes us very proud of what we mean to them."
The couple started by fostering an 18-month-old girl called Cheryl in 1977 – before they went on to look after more and more young people in the county.
Gillian, aged 74, said: "Fostering has been part of our lives for so long now and I’m sure I’ll miss it. I’ve loved every minute, even the challenges.
"The only part I really struggled with was sometimes handing the children back after looking after them.
"This was the hardest thing for me but knowing the difference I had made to their lives made it all worthwhile."
Jai Bradfield, from Doxey in Stafford, joined the family when he was 13 – and was due to stay for 12 weeks, but instead he stayed until he was 18.
The now-41-year-old, who is still in regular contact with the couple, said: "Neville and Gill are amazing people and I don’t think I’d be where I am today without them.
"I had other short term foster placements growing up but when I arrived at Neville and Gillian’s house I knew that’s where I wanted to be.
"From the outset I got love, support and encouragement all the way. I still call them mum and dad, because that’s what they are to me and always will be.
"I’m 41 now and am married with six children, plus I have two businesses of my own to run. When I need any advice, whether about one of the children or something to do with the business, I won’t hesitate to give Neville a call. He’s always there to listen and to offer words of wisdom."
Andrew Banks, now aged 19, joined the family when he was six years old and still lives with both Neville and Gillian as he trains to be a car mechanic.
He said: "Neville and Gillian have been so kind to me and I’m totally grateful for what they did.
"Not only did I have a loving family, which I never had before, but I got support and encouragement in every aspect of my life.
"I’ll never forget Neville’s words, ‘of course you can do it Andrew!’ And he was right."
The couple's retirement coincides with the launch of Staffordshire County Council's fostering service's campaign to recruit a further 60 foster families over the next year.
Councillor Jonathan Price, cabinet member for education and SEN at the authority, said: "Neville and Gillian are an amazing couple who have helped change the lives of many children in their long career as foster carers. I would like to thank them for everything they have done and wish them well on their retirement.
"Fostering can be a hugely rewarding experience and you see how you make a real difference to children’s lives. It can be challenging at times but it has some wonderful moments and experiences as well. We’re always looking for more foster families, just like Neville and Gillian so if it is something you might be interested in then please get in touch with the team."
People interested in becoming a foster carer can find out more at care4child.org or by calling 0800 1692061.