"Watching our children growing up into loving and caring little people is fantastic. They are our world," she says. "I am so happy."
Because while the Wolverhampton-raised athlete may have five gold medals and six Olympics under her belt, motherhood was the one dream she never thought she would achieve. She didn't marry until she was 54, and having previously undergone three unsuccessful rounds of IVF treatment in her 30s and 40s, it looked like it was not going to happen. But in 2014, at the age of 58, Tessa and her husband Densign White adopted their twins.
"When I used to think I'd never have children, it felt like a piece of me was missing. The emotional pain was very, very hard," says Tessa,.
"I'd always wanted children so much, I have a big family and when I wasn't falling pregnant I thought: 'Am I going to be the only one without children?'"
Now, to mark National Adoption Week, the former javelin thrower and heptathlete – who has also lived in Telford – is urging more people to follow in her footsteps by offering a home to youngsters in need of a loving family.
There are more than twice as many children in England waiting for adoptive families than there are adopters, new figures show.
Latest statistics show there are 4,140 children in England awaiting adoption, while just 1,700 families have been approved to adopt.
The figures from the Adoption & Special Guardianship Leadership Board show that of the children looking for new parents, 28 per cent are over the age of five, with four per cent suffering from a disability. It also reveals that 57 per cent of these youngsters have brothers or sisters, which the adoption agencies obviously wish to keep together.
A fifth of the children are also from ethnic minority backgrounds, and Tessa is keen to encourage more black and Asian adoptive parents to come forward.
"So many kids need to be adopted and a lot are black kids," says Tessa, who is now 63.
"Many have come from difficult backgrounds. We have to nurture them. But it is a very fulfilling, heartfelt thing to do."
Almost immediately after getting married, Tessa and Densign signed up as potential adopters with the Barnardo's charity. They then registered with a fostering agency, offering to look after children of school age, but in January 2013 were asked if they could take in twin babies. A few days later they were introduced to Cassius and Ruby Mae.
"I was elated, it was like winning a gold medal," says Tessa.
"Dens picked Cassius up and he fitted in his left arm. There was an immediate bond."
The children were just four months old, and had not had an easy start in life. Born prematurely to parents with drug abuse issues, and there were concerns about their future health. But while there were ups and downs, the couple have never looked back, and the twins now lead healthy and happy lives. Tessa and Densign, who is 57, formally adopted the children the following year.
She says giving the youngsters a fresh start has been difficult but rewarding.
"It's not about luck, it's about nurturing," she says.
"We are not perfect parents, but we are committed to helping our children recover from their early experiences."
Joe Lumley, of Adoption UK, says there are many false preconceptions about who can adopt children, but in reality there are only three requirements: you must be over the age of 21, must have been legally resident in the UK for at least 12 months, and there must be nobody in your household with convictions for offences against children or serious sex offences.
"It doesn't matter if you are gay, straight, or transgender, it doesn't matter if you are employed or unemployed, it doesn't matter if you live in a small house, and it doesn't matter how much you earn," he says.
Mr Lumley says there is a particular need for people to give homes to older children and those with disabilities.
He says the majority of children waiting for adoption have suffered either neglect or abuse, and this can manifest itself through problems for the children in later life. But he says there is plenty of support to help parents through these stages.
Mr Lumley says Adoption UK is particularly keen to find parents for older children and those with disabilities.
"We find that many people don't want seven- or eight-year-old children, they want babies," he says. "We are trying to persuade more adopters to consider to providing older children with a good home.
"We want to show them that, with the right support in place, adoptive parents can make real difference to children who have had a very difficult start in time."
He adds that there is no reason why people in their 50s and 60s could not adopt – as Tessa has done – providing their health is good.
"It all comes down to the health of the individual," he says. "Some people in their 50s and 60s are in better health than those in their 20s or 30s."
"It's not too old at all," she says. "You do need to think about how energetic you are, are you active enough, whether you are healthy, whether you can be out there doing things with the kids.
"It's not easy, but it's great."