The couple were only 33 and 35-years-old when they became grandparents for the first time in June following the arrival of baby Isla-May.
Jenni, now 34, shared: "When we are out with Isla everyone just assumed that she is mine and Richard's daughter.
"When we explain to them that we are actually grandparents they get the absolute shock of their life. Most people don't believe us when we tell them.
"But I can obviously understand why people would think we are her parents as we are still in our early thirties," she added.
"When Charmaine first told us that she was pregnant and that we were going to become grandparents we were really shocked.
"It has been a whirlwind but we love our new roles. I'm Nanna and Richard is G'pa.
"Being young grandparents just means you have more time to love your grandchild and longer to cherish them. And we might even get great-grandchildren."
After becoming a teenage mum herself, Jenni said her priority was to support her daughter, Charmaine, 16, as she understood what she was going through.
"I think she has even more respect for me now as her mum," she reflected. "We all live together under one roof too which is lovely.
"She's still with the baby's dad and they've been together almost two years, so Isla also has all of his lovely family. We look after Isla quite often to give Charmaine a break.
"I think it's brought us all even closer. My other girls absolutely love having a baby in the house, they love having a niece."
Jenni, who also has two other daughters, Chelsey, 13, and Scarlett, 10, added that it isn't "fair" teenage mums are stereotyped, having started a cleaning business following Charmaine's birth.
The mother-of-three explained that having a baby pushed her to succeed and hopes that example will inspire new mum Charmaine, who has been in a relationship with her boyfriend for two years, to follow suit.
Jenni continued: "Charmaine has watched me go to work and do well for myself while bringing her up, so she knows it's possible.
"She wants to go to college and do beauty. There is a stereotype about young mums which I don't think is fair.
"You can still enjoy your life and achieve whatever you want even if you have a baby when you're younger.
"I am glad that I am able to show my daughter that everything can still work out for you."
What a gorgeous family!
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