Burglars struck at the Top Munch cafe in Station Road, Strood, during the early hours of Tuesday morning and stole about £5,000 plus about £180 for the charity.
The cafe, which has been run by Medway boxer Brian Sanders for the past five years, was raising money for to send Winnie Martin, for treatment in America as she is suffering from Leukemia.
Winnie, from Aylesford, has Down’s Syndrome and a string of other serious medical problems.
The break-in happened at about 12.40am when one of the burglars got into the cafe through a window.
CCTV footage shows him entering Mr Sanders’ other business above the cafe, a tanning shop, and letting his accomplice in through a fire exit.
They stole stock, about £2,000 of takings and about £3,000 from Mr Sanders’ boxing ticket sales, much of which he was going to donate to Cancer Research UK as his dad is suffering from the disease.
Mr Sanders, 38, who also sponsors other Medway amateur boxers in their bouts, said: “They took all my ticket money and the takings.
“I never leave cash in the place overnight, this was a one off and it was in a locked cabinet.
“They also took the charity money for the little girl, which is heartbreaking.
“I’ve called her mum to tell her and have pledged to give them £100 from every one of the fights I do in the future to make up for it.
“I can’t see the little girl go without and her mum was happy with that.”
The thieves also smashed up a coffee machine and a sunbed in the tanning shop above.
Mr Sanders, “This is my livelihood. I employ three girls, they are like my family it’s their livelihood too.
“We had to remain closed on Tuesday so we could clean up, but I hope we will be back open soon.”