West Mercia Police said it happened at about 4.30am on Saturday, December 15, in Albert Road.
The teenagers stole a crate of milk and then made off in the float which crashed into another vehicle in Albert Road.
Officers are appealing for information about the two boys and a girl, believed to be about 15-years-old, who carried out the attack.
Anyone with information should contact police on 101 quoting the incident number 0125s151218.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or online at crimestoppers-uk.org