The group of about 40 people punched windows and tried to kick down glass doors at Liverpool's Titanic Hotel at about 22:10 BST on Friday.
City mayor Joe Anderson was hosting the event in aid of For James - the fund set up after he was killed in 1993.
Merseyside Police are trying to identify those responsible.
The force said about 12 people, believed to be anti-austerity protesters, managed to enter the reception area of the hotel, smashing a window and breaking a fire door.
Security staff managed to remove them from the premises and police were called.
However, the gang fled and no arrests have been made.
Mr Anderson said James Bulger's mother Denise Fergus was left "in tears" after the disturbance during the meal, which raised Â£21,000 for the fund.
He said: "I thought it was disgraceful. Their behaviour and intimidation, and the way they conducted themselves.
"They damaged the building, a window was smashed, they frightened people.
"Denise was in tears. We were trying to raise money for her charity in James Bulger's name. It helps disadvantaged kids.
"These thugs abused people and tried to disrupt what was going on."
Assistant Chief Constable Chris Armitt said: "Whilst Merseyside Police will facilitate peaceful protest, we will not tolerate criminal activity, or aggressive and intimidating behaviour towards staff or customers at local businesses.
"We are currently carrying out an investigation into last night's incident in a bid to identify those responsible for the criminal damage and to ascertain if any other crimes were committed."
A spokesman for the Titanic Hotel said the damage was "minimal" and staff will be taking no further action.
A group of political protesters broke into a hotel during a charity dinner to raise money in memory of murdered toddler James Bulger.