"The family are mongrel mob so are used to intimidating people. Your staff didn't care. They just wanted to ensure the young girl felt safe.
"And to all those members of the public who stopped and helped. THANK YOU".
Senior Sergeant Matthew Tiernan confirmed to One News that police were called to the mall on Sunday.
Tiernan praised staff saying they did the right thing in calling police and keeping the child safe.
A 51-year-old woman has been charged over the incident.
Williams' post on Facebook has since gone viral with more than 9600 reactions, 400 comments and 330 shares.
Big UPS to your staff at Eastgate ChCh today. A young girl was being beaten by her father and then her grandmother this...
Posted by Jo Margaret on Saturday, 6 May 2017
"Well done Warehouse staff Eastgate, I'm glad that little girl had caring people who went, that extra mile to protect her", one person wrote.
"Wow, thank you to everyone involved in protecting this girl. We all need to step up and take action, not walk away. Save the kids", another said.