The burglars broke into the Kings Heath store overnight between June 7-8, damaging doors, tills, computers, and even raiding a donation tin.
But since the raid supporters have rallied together to raise the huge sum for the hospice.
Acorns chief executive Toby Porter said: “The response to the news that one of our shops had been burgled and vandalised has been truly heartwarming.
“The purpose of our 45 Acorns charity shops is to generate the funds we need to provide our vital children’s hospice care.
"Facing significant costs repairing our Kings Heath shop, we are thrilled and humbled to announce that hundreds of amazing supporters have made donations via our website and a special JustGiving page, and together they have donated a total of just over £21,000 in 24 hours.
“It costs £7,000 to fund all of the costs of one of our children’s hospices and their family services for a day. So this response to this one shocking event is now going to pay for three full days of world-class children’s hospice care at one of our hospices. From the bottom of our hearts, thank you!”