Selfless youngsters took on inflatable obstacles and mud-filled pools along a 5km track in order to raise funds for Cancer Research UK.
The race preceded another Pretty Muddy event for adults held on the Saturday afternoon, to be followed by the Race for Life events on Sunday.
Among those taking part were Stamshaw siblings Ben, Isla and Hollie Parkfield who were taking on the challenge for both their nannies – one who died of cancer and the other, Alison, who is currently battling it.
10-year-old Ben said: ‘I’m racing to cure cancer.
‘I’m looking forward to the race.’
Their grandmother, Alison Levesque, 57, added: ‘I’m really proud of them all.’
At the time the trio had raised more than £200 for the cause.
11-year-old Brooke Newbrooke, from Gosport, was also there to run with her siblings Frederick, aged five, and Seth, eight.
Her mum Dolcie and nanny Shirley were there to take part in the adults’ race later in the day.
Combined the family had raised £110 in memory of Brooke’s great-grandfather who died a few years ago.
'I'm excited. I'm looking forward to getting muddy and doing all the obstacles,’ she said.
'And it's important to raise as much money as possible because there are lots of children getting cancer who need our support.'
Seth agreed. He said: 'I'm most excited for getting muddy. '
Frederick added: 'We're going to have a hot cocoa afterwards and going to watch Mum and Nanny.'
It was a father-son effort for five-year-old Regan Snagg from Fratton.
He was running with his dad Raymond for his grandad who recovered from non-Hodgkin lymphoma.
Regan, who had raised £150 so far, said: 'I'm looking forward to the slide and the mud.'
Keen runner Betty Holman, nine, said the Pretty Muddy event was the first time she’d taken part in a race like it.
The Liss Forest resident said: ‘I’ve done Park Runs before but not this.
‘I’m really looking forward to it, especially all the obstacles and getting muddy.’
Around 1,200 people took part in both the children’s and adults’ Pretty Muddy races.