Misael Caldogno Abreu is three times the size of other children his age due to a syndrome which means he is unable to stop eating.
He is so heavy he often stops breathing while sleeping - leaving his terrified parents fearing that one day he may not wake up.
Doting dad Manoel Abreu, 38, said: "Everything is hard for him - he is a baby carrying an adult’s weight.
"His heart must be suffocated and working under a lot of pressure. If he doesn’t get the treatment he requires there is a very good chance he will pass away."
Misael, from Espirito Santo, Brazil, was born a healthy 6lb 6oz, but immediately started piling on the pounds.
Doctors believe he may be suffering from Prader-Willi syndrome, a rare genetic condition that leaves him with an insatiable appetite.
He now weighs a hefty 178lb (12.5 stone) and is still gaining despite following a low-fat diet and walking for 40 minutes each day.
Despite their constant struggle his parents have refused to give up on him, and say they will do anything they can to improve his quality of life.
Mum, Josiane de Jesus Caldogno Abreu, 37, said: "He has been putting on a lot of weight since he was a baby - even when I was breastfeeding him it was more than expected.
"But it was only when he was one and a half years old that we began to worry. He was gaining 3kg (6.6lb) a month and was starting to get very heavy.
"His situation is complicated. We know we could lose him at anytime.
"Sometimes when he is sleeping I watch him to see if he is breathing.
"I cry a lot because we want to help him. But I am also very proud of him because he is a child who doesn’t surrender.
"I live for my son - he is so special. His teacher told me that everything the other children do, he wants to do as well.
"He doesn’t want to have limits. He wants to be a normal child."
Misael visits a doctor every three months to try and control his condition but currently there is no cure for Prader-Willi syndrome.
Paediatric neurologist Lucio Coelho Miranda said: "Every appointment we have had he has put on a lot of weight - sometimes up to 5kg (11lb).
"I think Misael could get help from someone outside of Brazil - both medically and financially - so he can get the laboratory and genetic testing he needs."