Almost half of the places in a new children's fun run have been snapped up in less than a week.
The YEP-backed Jane Tomlinson Arena Junior and Mini Run was only launched last Wednesday.
But already more than 400 of the 1,100 available free places have been allocated.
Mike Tomlinson, who is organising the event as a tribute to his late wife and cancer campaigner Jane, said: "It's phenomenal.
"We're really pleased that it seems to have grabbed the imagination of children, their parents and their schools.
"We've been overwhelmed by the support and if we carry on like this, the runs will be full in no time.
"Children who want to run need to get their entries in quickly."
The run is the biggest free event of its kind in the UK. Entry fees have been waived thanks to sponsorship from city print firm Arena.
The company's Adrian Fitzpatrick said: "It is a great honour for Arena to be associated with the inspirational Jane Tomlinson and her appeal and we are delighted to be able to help make Jane and Mike's dream come true by removing the cost barrier, allowing each and every child the chance to run, have fun and hopefully get bitten by the healthy living bug."
The event, on May 9, is part of the Leeds Half Marathon and comprises two individual runs: one of 1.5km for three to eight-year-olds and one of 2.5km for nine to 14-year-olds. While the event is entirely free, those taking part are encouraged to raise a small amount – around 10 – for a charity of their choice.
Money donated to the Jane Tomlinson Appeal will go towards a new play area at the paediatric X-ray unit at Leeds General Infirmary, where Jane used to work.
As well as 400 entries, Mike said he had already received donations of 500 towards the cause.
He added: "It's great that children and their families are already donating money, even before they have taken part."
The Jane Tomlinson Arena Junior and Mini Run was the brainchild of Rothwell mum Jane, the campaigner and fundraiser who clocked up a series of incredible feats despite battling terminal cancer.
She died in September 2007, before the inaugural children's run could be held last year.