The 23-year-old - who surprisingly edged Barcelona team-mates Xavi and Andres Iniesta for the 2010 world player of the year award - said that he realised he was being well paid for what he did but he couldn't shake off his old childhood habits.
"I have changed nothing, my style of play is still that of a child," said Messi, who in contrast to Xavi and Iniesta had a disappointing World Cup as Argentina were well beaten by Germany in the quarter-finals.
"I know that above all it is my job and that I should approach it in another way, but one must not lose sight of the fact that football is a game.
"It is imperative one plays to amuse oneself, to be happy. That is what children do and I do the same thing."
Messi, who is equal top scorer with Cristiano Ronaldo in the Primera Liga with 24 goals this term, revealed that he does have moments of self doubt, belying his usual placid temperament he displays on the pitch.
"When I am angry, I go into my shell, I become mad," he said.
"But that happens more often at home, alone, than on the pitch."
Messi said he enjoyed playing centre forward far more than where he had been slotted in on the wing when he first started.
"I began playing in this position last season and it is the ideal spot, because virtually all of our play at Barcelona comes through the centre," he said.
Messi said that he ignored the criticism he had received for what are seen to be below-par performances for the national side and his superlative form for Barcelona.
"Yes, that (criticism) annoyed me.
"But, happily, these criticisms are behind me.
"I am now very at ease in the national side and would like to win the World Cup one day.
"As far as I'm concerned, you are never really a great footballer until you have won one."
Messi also dismissed any comparions between himself and legendary compatriot Diego Maradona, who almost singlehandedly inspired Argentina to the 1986 World Cup trophy and coached Messi and his countrymen at the 2010 World Cup.
"Argentina has been searching for a long time for a successor to Diego.
"There was Pablo Aimar and then Javier Saviola... But there is only one Diego and it is illusory to want to have another one."