The toddler was in a pushchair with his family in a Worcester shop when a corrosive substance was "thrown or sprayed" over him, according to West Mercia Police.
-> Suspected acid attack was 'pure evil'He was treated in hospital for burns to his face and one arm before being released on Sunday afternoon.
Chief Superintendent Mark Travis said the boy is recovering at home with his family, who are being supported by specialist officers.
He told Sky News: "A young family were out shopping and a substance appears to either have been thrown or sprayed towards a three-year-old child who was in a pushchair."
He added: "We are uncertain about the long-term implications of those burns, but we do hope that these won't be life-changing injuries."
Ch Supt Travis renewed the appeal for information about three men seen in images released by police.
-> Devastated victims of £10,000 Leeds house burglary release CCTV footage of suspect"We are really, really keen that the images we have released will hopefully bring forward information about people who maybe able to help us, who were in the store at the time of the incident.
"If those people can come forward or people could identify those people it will help us understand the motivation for this."
He said the men were in the shop at the time of the attack and were "in very close proximity to the little boy".
They left the store in the direction of the city centre and he urged anyone who has seen "anything discarded in the area" to come forward.
A 39-year-old man from Wolverhampton has been arrested on suspicion of conspiracy to commit grievous bodily harm and remains in police custody.
Worcester City Council leader Marc Bayliss described the attack as "absolutely pure evil".
-> Police helicopter apologises for noise over Leeds after apprehending two burglarsHe added: "I have never heard of an acid attack in Worcester so this is absolutely not something we have any experience of."
Worcester MP Robin Walker said the attack was "horrific", and added: "The shock will be universal, anyone conducting such an attack on a small child is just appalling."
The incident occurred at around 2.15pm on Saturday in the Home Bargains store on the Shrub Hill Retail Park in Tallow Hill.
West Midlands Ambulance Service said a crew arrived at the scene in eight minutes and "liaised with the trust's hazardous area response team for specialist advice".
A local shop worker, who did not want to be named, said he saw a number of emergency services at the store on Saturday and two police officers were stationed outside on Sunday.
The deputy leader of Worcester City Council, Adrian Gregson, said he was in the shop next door shortly after the attack.
He told the Press Association: "I was in the shop next door when it was going on, it was around mid-afternoon.
"There were a couple of fire engines and a fire incident vehicle and a police car."
A Home Bargains spokeswoman said: "Our thoughts are with this young child and his family at this very difficult time."