The suspects, aged 22, 25 and 26, were detained in London on suspicion of conspiracy to commit grievous bodily harm, West Mercia Police said.
A 39-year-old man from Wolverhampton arrested on Sunday on suspicion of conspiracy to commit grievous bodily harm remains in custody, the force said.
The toddler was in a pushchair with his family in a shop when a corrosive substance was "thrown or sprayed" over him on Saturday afternoon, according to West Mercia Police.
Canon Georgina Byrne from Worcester Cathedral told Premier News Hour the community was shocked to hear about the incident.
"Worcester is a very peaceful city and I'd have to say it's quite an extraordinary event in the life of the city so people are concerned and upset about it," she said.
"But we're aware police are dealing with things at the moment so I think people are comfortable that something is happening."
The toddler was treated in hospital for burns to his face and one arm before being released on Sunday afternoon.
Police said the long-term implications of his injuries are "uncertain".
Canon Byrne has asked people to pray for the situation.
"Pray for physical healing and for a swift physical healing," she said.
"Pray for the medical staff and I would encourage people to pray for inner healing and comfort for someone who must be quite frightened."
Worcester City Council leader Marc Bayliss described the attack as "absolutely pure evil".
Worcester MP Robin Walker said the attack was "horrific", and that the "shock will be universal".
Canon Bryne added: "It's a very extraordinary event in an otherwise peaceful city.
"We're not thinking there's a crime wave or anything in Worcester. It's a matter of keeping people calm and reassuring people of the goodness that's going on - there's a lot of good things going in Worcester at the moment."
Police are continuing to appeal for information over the incident at Home Bargains in Tallow Hill.
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