My twin daughters are four years old but this month they will celebrate their very first birthday.
The girls are 'leaplings' – people born on February 29, a day which happens only once every four years.
Leap day dates back to 1582, when Pope Gregory XIII solved the problem of the ancient Roman calendar falling out of step with the changing seasons, by adding an extra day to every fourth year.
I'm a bit hazy on the details, but it appears that without his intervention Christmas would have eventually collided with Easter, causing a chocolate overload from which no New Year's resolve could ever have recovered.
Ever since, February 29 has occurred in (almost) every year which is divisible by four, making 2012 a leap year and giving my twins their first ever birthday.
I went into labour in the morning of February 28 2008, amid lots of midwife banter about just missing Leap Day. Twenty-four hours later I was still in the delivery suite and the girls were born just after eight o'clock on the 29th.
The odds of being born on a Leap Day are one in 1,461, so although it's not exactly rare, it's still enough of an oddity to be interesting. It's always fun telling people when the girls' birthday is, and surprising how many people know someone else born on a Leap Day.
The first time I met our elderly neighbour, long before the twins were born, he told me with glee that he was married to a 16-year-old. He cackled at my raised eyebrows, before introducing me to his wife Alice, who had another 48 non-leap-year birthdays to add to her 16 'proper' ones.
She rolled her eyes at the well-worn joke but admitted she rather liked her special status. "It's the one way I can legitimately shave a few years off my age," she smiled. There are more than four million Leap Day babies in the world, including celebrity 'Leaplings' such as singer Dinah Shore, rapper Ja Rule, and actor Anthonio Sabato Jr. There's even a member of the Royal Family in the Leap Day club: on February 29t 1964 the Queen's cousin, Princess Alexandra, gave birth to her son James, at the time 13th in line to the throne.
With no official birthday in three years out of four, my girls will have to decide when they would rather celebrate. The first year we opted for February 28, the second March 1, but neither day really felt right.
Last year they chose to have their birthday on different days, which I suspect will be the norm as they grow up. This year they'll be having a joint party where they and their friends will be 'leaping' around in celebration of the special date.
My friend Anna's oldest son Jenson was born on the same day as my daughters and, like me, she's looking forward to Leap Day. "We usually celebrate on the 28th February," she says. "It seems bizarre to me to consider celebrating his birthday in March, but this year we will definitely be making an extra special fuss.
"When we realised in the early stages of my pregnancy that the impending arrival may just be a Leapling I was gutted but only for the baby's sake - how unfair, I thought, to only have a birthday once every four years.
"But when I went into labour in the early hours of the 29th I became excited at the thought of having a baby on such a momentous day. As our much-longed-for darling son was delivered into my arms I was truly elated to realise that his birthday is nearly as special as he is."
The legal stand-point on Leap Day birthdays varies from country to country. In China, for example, a Leapling legally turns 21 on February 28, yet Hong Kong statute stipulates March 1 as the 'official' birthday.
It's a few years until my daughters are on the cusp of being able to drive, vote or drink alcohol, but I imagine they'll be very relieved to discover that in the UK they'll turn 18 on February 28 2026 and won't have to wait that extra day for their first legal drink!
Were you born on February 29 or do you have a leap year child?