I think am interested in becoming and elementary school teacher.
This is school  for children between the ages of 4–11 and coming between pre-kindergarten and secondary education.
Do you know if it is the same worldwide? 
Yes it is, as at 2001 there there were 92,858 elementary schools (68,173 public, 24,685 private) in the USA
I think elementary school is very important for the child development, do you know what are the most important subjects tough there?
Yes it especially from  from grade one through grade eight.
I wonder what would be the requirements to became and elementary school teacher. Do you have any idea?
The curriculum covers basic arithmetic and sometimes rudimentary algebra in mathematics, english proficiency so a teacher would need to be a certified teacher in these areas
And how can I become a certified teacher?
In not too sure , but first step would be to get skill that  introduces  children to the broad range of knowledge, skill and behavioral adjustment