Dexter Neal died after he was mauled by an American Bulldog, while playing with a friend in Parker Way, Halstead, Essex, in August 2016.
Jade Dunne, 29, formerly of Parker Way but now of Colchester, appeared before magistrates in Colchester on Tuesday.
She was released on bail until she is sentenced at Chelmsford Crown Court on 16 May.
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Dunne admitted a single charge of owning a dog that was dangerously out of control causing injury resulting in death. Her American Bulldog, called Ruby, was later destroyed.
Dexter, who lived in Ronald Road, Halstead, was airlifted to Addenbrooke's Hospital in Cambridge after he was bitten at Dunne's home.
At the time, neighbour Phyllis Young told the BBC that she had heard "screaming" at the time of the attack.
"I did not really associate it with anything terrible - it was like children having a bit of fun," she said. "But then I thought it might not be quite right.
"I looked out of the window and saw a police car and paramedics and neighbours looking along the road."
Shirley Diver, mayor of Halstead, described the incident as heartbreaking.
Following news of Dexter's death, she said: "It's so sad. I feel so sadly for the family who are involved.
"Words can't express how it affects anybody. The whole town is in shock."
A woman has pleaded guilty to owning a dangerously out of control dog which killed a three-year-old boy.