Sonny Rees drank the 40% proof whisky at his second birthday in a Frankie and Benny's restaurant in Swansea.
His mother Nina Rees, 34, only realised the mistake after he had finished the drink and had taken photos of him drinking it.
Sonny, from Pontarddulais in Swansea, was taken to accident and emergency where he was kept under observation by doctors.
He's now recovering at home. The restaurant is investigating how the incident happened.
Nina said: "We went to the restaurant just after midday and I had ordered him lime juice and water, his favourite.
"The drinks arrived and I was encouraging him to take sips because he was eating salty things.
"We had finished our first course when we noticed he was pulling a face as he was drinking.
"I took it from him and took a sip myself. It was whisky, I would say a double. As soon as I sipped it I had the slight burny feeling in my throat and warming in my chest.
"Sonny had taken about 10 sips - he was obviously intoxicated.
"I immediately went into a panic and a rage - I was crying my eyes out."
Nina complained to the manager who took a sip herself but she wasn't happy with the staff's reaction and called NHS Direct before taking Sonny to accident and emergency.
Sonny was asleep by the time he arrived at Morriston Hospital, Swansea, where staff monitored his vital signs.
He was later given the all-clear and allowed to go home.
A Frankie and Benny's spokesman said: "The company is incredibly sorry for what happened. It was a human error and we are putting measures in place to ensure it never happens again."
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