Charlotte Garside is two years old but weighs just 7lb 8oz - the size of a newborn baby. At 58cm tall, she's smaller than many of her toys and wears newborn dresses.
She will never grow taller than 2ft, due to a rare type of primordial dwarfism that has delayed her growth and development.
When she was born she weighed 1lb 1oz and her parents had to dress her in clothes made for dolls.
Charlotte's mum Emma Newman, from Withernsea, near Hull, says: "We've had so many tests and so many results, but so far all we know is that she has some type of primordial dwarfism – the Charlotte kind.
"We have spent a long time trying to find out what makes her different and what we can to do help her.
"But all we know is that Charlotte really is one of a kind. She's been through a lot in such a short life.
"So many tests and hospital visits, but she takes it all in her stride. There are no definites so we don't know how long Charlotte will be with us. We hope for as long as anyone else but we just don't know.
"We're just enjoying family life. She might be small but anyone who has ever met her will tell you that she has a big personality. Since the day she was born, she has brought something very special into all of our lives."
Extraordinary People: the Tiniest Girl in the World, 9pm, tonight, Five.There were no signs of Charlotte's condition until she was born in August 2007.
Emma, 28, from Withernsea near Hull, already had three daughters Chloe, 13, Sabrina, 10, and Sophie, six and all of them, together with builder dad Scott Garside, 24, were looking forward to the birth.
Emma says she had a big baby bump and all the scans seemed fine. But when she went into labour doctors said she must only be 24 weeks pregnant - although she knew this was not possible.
Emma explained: "The doctors said to be prepared for the fact she was going to be very small. I thought they meant three or four pounds."
After a few days, Charlotte was diagnosed with Majewski osteodysplastic primordial dwarfism (MOPD), a genetic condition.
Doctors don't know how long she will survive, but at the moment she is in good health and her mental development is fine. She's almost walking and will soon be talking.
Emma told the program: "She means the world to us and as you can see she is raring to go. She just wants to join in and follow her big sisters everywhere.
"She is such a driven, determined person. Our next big event is her third birthday in August, we're planning a big party here. A real celebration. We've stopped thinking about the what-ifs, now we're having the best time we can."
The family is featured in a TV programme "Extraordinary People: The Tiniest Girl in the World", on Five tonight at 9pm