LONDON (Reuters) - Britain's Prince William and his wife Kate would seek help for their children George and Charlotte if they had mental health problems one day, Kate wrote in a blog published on Wednesday that sought to tackle the stigma associated with mental illness.

Acting as guest-editor for a day of the Huffington Post UK news website, the former Kate Middleton commissioned a series of articles on mental health issues affecting children and young people, introducing the project with her blog.

"Parenting is hard enough without letting prejudices stop us from asking for the help we need for ourselves and our children," wrote Kate, whose official title is Her Royal Highness the Duchess of Cambridge.

"Like most parents today, William and I would not hesitate to seek help for our children if they needed it. We hope to encourage George and Charlotte to speak about their feelings, and to give them the tools and sensitivity to be supportive peers to their friends as they get older."

Kate's marriage in April 2011 to William, who is second-in-line to the British throne, was a global media event, as were the births of the couple's children Prince George in July 2013 and Princess Charlotte in May 2015.

The photogenic Duchess is rarely absent from Britain's front pages, but the popular royal couple give little away about their private lives, heightening public interest.

Kate has campaigned on the issue of children's mental health since the early days of her marriage, in the hope that her association with the cause would help break down social barriers that prevent people from opening up about their problems.

Her guest-editorship of the Huffington Post comes at a time when deficiencies in the provision of care for mental health patients in Britain's National Health Service have been in the headlines.

Prime Minister David Cameron said in a speech last month that almost one billion pounds ($1.4 billion) would be invested to enhance mental health services, although critics said the measures announced were insufficient to fix the system.

($1 = 0.7004 pounds)

(Reporting by Estelle Shirbon; editing by Kate Holton)