Albie Speakman was struck by the vehicle in a freak accident at Tottington near Bury, Greater Manchester.
Despite the best efforts of paramedics he was pronounced dead at the scene.
In a statement issued through Greater Manchester Police, his mother Leah said: “Albie was an incredibly loving, affectionate and caring boy who just wanted everyone to be happy.
“He was so sensitive and wanted everyone to be ok, especially the people that he loved.
“He loved to play – whether it be with his family or friends at nursery – he would always look for little round things wherever he went, stones, polystyrene balls, bouncy balls, beads – I’m not sure why but he just loved anything round, he would just hold onto them.
“His favourite memories are at Cleethorpes beach, with his bucket and spade and his ball. His happiest days were on that beach, we were so free and didn’t have any cares in the world.
“It was just me and Albie and nothing else mattered. Whenever I’d ask him what he wanted to do, he’d want to go on holiday to the beach again; that’s how I know he was truly happy there.”
The statement from Albie’s mother continued: ““We all love Albie so much more than we can ever put into words – especially his Nan and his ‘Nanny-Nanny’, as he would always call her.
“I will miss absolutely everything about Albie, his voice, his smile, the smell of his skin and the feel of his little hands on my face when he would say ‘I love you mummy girl’.
“…I’m not sure how to carry on this life without you but I will find a way to be strong for you and make you proud.”
The driver of the tractor is assisting officers with their enquiries while police investigators work alongside the Health and Safety Executive to find out why it happened.
Chief Inspector Ian Partington, of GMP’s Bury district, said: “Despite his family flagging down an ambulance while driving him towards hospital as quickly as they could, the boy sadly could not be saved after the best efforts of paramedics. I can’t imagine how distressing this was for those involved.
“We are working to ensure that a full investigation is carried out, and the farmland where we understand this incident to have occurred remains cordoned off to allow our investigators and partners from the HSE to conduct thorough inquiries to establish exactly what has occurred here.”
A police car was involved in a minor crash with another vehicle in Bell Lane while officers attended the initial call from the North West Ambulance Service.
The occupants of the second vehicle were taken to hospital as a precaution.
The officer in the police car was unhurt.