The theft took place shortly after 2.15pm on Sunday afternoon.
BoomChikkaBoom is a local party planning business which covers events ranging from children's parties to weddings and Bar Mitzvahs.
Speaking to the YEP, organiser Faye Kenny explained what had happened.
"I was in town and Holly who works for me was in Roundhay. The family were on their way to the venue so Holly unloaded the equipment into the entrance of the church, then moved the car," she said.
"She moved the car about five metres away and while her back was turned the equipment has been taken from the entrance of the hall."
Neighbours reported seeing a scrap man on the road moments before the equipment was taken.
Equipment taken included a music system, multiple lights, bubble machine and a snow machine. The thief even took the shakers.
"Please return the equipment so that we can continue to make children in Leeds happy because you ruined a six-year-old's birthday party on Sunday," Faye added.
BoomChikkaBoom has since launched a GoFundMe campaign which smashed its £1,000 target within 45 minutes of going live.
The campaign has since been suspended by the site for breaching its terms of service.
CCTV of the incident has been passed onto West Yorkshire Police.
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