The boy was left with severe burns on his face and arms after the police assumed it was a "targeted attack" on Saturday afternoon.
The police released CCTV photos of three men on Sunday who they would like to see related to the incident, adding, "They can have vital information for the investigation."
"At this time, we treat this as a targeted attack on a three-year-old boy," police chief West Mercia Superintendent Mark Travis said in a statement.
"The incident will deeply shock the local community and I would like to assure the locals that we are conducting a thorough investigation to identify those responsible, at which time the motive for the attack" It is unclear. The officers are working hard to pinpoint what happened and what the substance is. "
Worcester local Parliament member Robin Walker described the incident as" horrific. "
" The shock will be universal Anyone con with such an attack on a small child is simply frightening, "he told the press association.
" It is a topic that rightly caused great concern in parliament and exacerbated the punishment for any kind of acid attack.