A three-year-old by was crushed to death when a marble fireplace fell on him as he played at home.
Paramedics tried to save little James Curtis after the tragedy on Monday morning and he was airlifted to hospital from the house in Tranmere, near Birkenhead, Merseyside.
A neighbour said: "I heard his mum screaming in the front garden. I'd never heard anyone screaming like that so I knew something bad had happened.
"Then I realised she was screaming the child's name."
James's distraught mum Charlotte Edwards, 22, said on Facebook: "Words cannot describe how much love I have for him and always will.
"You will always be my number one boy and always be in my heart, absolutely devastated!
"James Stuart Curtis my whole world is now in heaven with my nan. I will see u again soon baby RIP love u millions."
In another post, mum Charlotte added: "James was and still is loved by millions and he loved every single person he met!
"We are who we are today because of our little boy and the past nearly 4 years have been the best of our life!! My whole world and my hero."
A Merseyside police spokesman said they were investigating the death and added: "Paramedics attended and took the boy to hospital where he unfortunately died.
"Officers are in attendance at the property as is normal procedure following the sudden or unexplained death of a child.
"An investigation into the full circumstances of the incident is ongoing."