My daughter Jemima is only a toddler, but she's already experiencing the gender pay gap. Because in the two years since she was born, I've spent more on her than I have on my two sons combined.

I'm not the only one - a study this month by Sainsbury's Bank found that parents spend £300 a year more on daughters than sons in their first five years. The average cost of raising a son until five is around £5,475, compared with £5,767 for a daughter. The difference increases to £400 a year between the ages of six and 13, and £600 a year between 14 and 18.

In my case, this is partly because Edward, who is four, inherited most of his belongings from his brother Charlie, seven - but mainly, it's because clothes and toys for little girls are so much prettier. I can spend hours browsing the girls' clothes department in John Lewis and the "pink aisles" of Hamleys, and I love splashing out on gorgeous dresses, shoes and sparkly hairbands. Sadly, I can't find the same sense of excitement shopping for my boys.

On a recent trip to stock up on towels, I came back with a Beatrix Potter book and soft, floral pyjamas from the White Company as a treat for Jemima. I didn't even think of picking up a gift for the boys.

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For her second birthday, my husband Dominic and I bought Jemima an extravagant mini designer kitchen from the Great Little Trading Company that cost £100, and a pretty party dress for £30. The boys, meanwhile, got toy cars and action figures to add to their collections at less than half the cost.

The disparity may also come down to the fact that girls' clothes are more expensive, says Ruth Harrison, director of retail strategy at ThoughtWorks Europe consultancy. "Retailers have identified a new trend of 'mini-me'," she says. "They are tapping into selling the add-on items, accessories such as bags, shoes, hair pieces and jewellery, which are fashionable among girls."

Parenting coach Elizabeth O'Shea, director of Parent 4 Success, believes it is also a result of a special bond that British mothers tend to form with their daughters early on. "Mums in the West tend to hanker after a little girl, as opposed to mums in the East, who often want sons," she says. "Daughters are often considered friends for life and we can project our own hopes and aspirations on to them. So we tend to invest more in elaborate clothes and outfits for them."

I suspect my behaviour is partly a result of my upbringing. Growing up, I felt my older brother received preferential treatment, not least because he was sent to a prep school, whereas my sister and I went to our local primary. My mother was also treated differently to her brothers - they were often given steak and chips, while she had cheese on toast.

Most of my friends are equally guilty of spoiling daughters. One spends £1,000 a year on Boden clothes for her daughter, but just £300 on her son, mostly from H&M. Another lavished £600 on a Frozen-themed party for her daughter's fifth birthday, with a real-life Anna and Elsa, but her son was taken to a go-kart track with three friends.

It sounds unfair, but I understand. I know that Jemima appreciates lovely things but the boys don't notice them. If they're fed and have (relatively) clean sheets, they're happy.

And it's not just clothes, toys and parties. When it came to decorating Edward and Charlie's bedrooms, each have a chest of drawers, Ikea blinds and a few Thomas the Tank Engine and Star Wars posters. But I got so excited when it came to Jemima's bedroom, I whipped out my credit card and bought candy pink and green blinds from Designers Guild, bespoke pictures, alphabet murals and a handmade wardrobe that I'm too embarrassed to admit the price of.

Dominic is just as guilty of spoiling Jemima, but one friend was horrified when she saw Edward in scruffy jeans while Jemima wore a pristine dress. I just shrugged and said he would happily walk around in a paper bag, as he doesn't care about clothes.

I sometimes worry that I'm overcompensating. I love all three children equally and I certainly wouldn't want Edward and Charlie to feel that they aren't as cherished as their sister. Nor do I want Jemima to feel she is superior. But I disagree with the idea that you should dole out the same to all of your children, given that they have different tastes.

After all, we may spend more on clothes and accessories for Jemima, but she gets the same amount of time, love and care as her brothers. I wouldn't have it any other way.