Daughters are more costly to raise than sons, according to a survey of parents.
From birth until the age of five, girls are around £300 a year more expensive a year than boys, Sainsbury's Bank found.
The cost gap doubles during the teenage years, with parents of girls aged between 14 and 18 typically forking out nearly £600 a year more than parents of boys of the same age, the research found.
The research suggested the gap may in part be due to girls' clothing being more expensive than that for boys.
The survey also showed that parents of children under the age of 25 estimated that, on average, just over a fifth (21%) of their monthly household income is spent directly on items for their children.
And the average parent expects to be supporting their child financially well into their adulthood - until the age of 29.
Mums typically think the cut-off point for financially supporting their child will be 30 - while dads are hoping it will be a few years earlier - at about 27.
Jasmine Birtles, founder of website MoneyMagpie.com, wrote a report on the findings.
She said: "I'm surprised that parents feel that even when small, their daughters cost more than their sons. Are parents buying more outfits for their tiny girls?"
More than 2,000 people from across the UK took part in the survey and parents were asked to estimate the annual cost of raising their children.
The research found that up to the age of five, the average annual cost of raising a girl is £5,767, while a boy is typically £292 a year cheaper, costing parents £5,475.
Between the ages of six and 13, a girl costs parents £6,794 a year, while a boy costs £6,414 - £380 cheaper a year on average than a girl.
And between the ages of 14 and 18, a girl costs parents £7,747, while a son costs £7,172 - making a boy £575 a year cheaper than a girl - according to the report.
Andrew Hagger, founder of Moneycomms.co.uk, who also contributed to the report, said: "Couples planning their first child may take a sharp intake of breath when they see the figures in this report but at the same time it provides an important reality check and an idea of what to expect.
"Whether it's a boy or a girl, household finances can be turned on their head when the first child is born - a sudden spike in expenditure and potentially less income means that the family purse needs to be managed more closely."
But despite the initial financial hurdles that come with having a child, many parents who had gone on to expand their brood said the cost burden was less severe for subsequent children.
Three-quarters (75%) of parents with more than one child said first-born children were more expensive to raise than their siblings.
Many parents had kept the costs of younger children down by reusing items such as toys, clothing, bikes and prams.
Simon Ranson, head of banking at Sainsbury's Bank, said: "Families can be expensive, but it's no surprise that the first child comes with the largest price tag. There's a lot that families can do to keep these costs down, for example reusing items such as prams and toys for subsequent children.
"And of course, fixed costs such as accommodation and utilities - as well as the cost of food - don't always change significantly when there's more than one small person in the house."