What do kids do first when they even learn to talk, still being less than 1? Yeah. They learn syllabes. Kids are born with unlimited sound repeating ability. They are going to develop their skills accordingly to requirements of their native.

Tamil language, being closer to nature, does not have only singular letters like languages that use roman alphabet; the language script (called scientifically as  abugida) contains "letters" that actually stand for syllabes.

There are 12 vowels (long and short) and 18 consonants, and each one "combines" with each other making an unique sign for each syllabe. There are as well some extra signs for letters that do not exist in Tamil as such (for example "j", "h", "s").

Generally Tamil language is undergoing some major transformations, because nowadays people are far from using its pure forms. I'm either not a professional linguist so I will not focus on these all small details;

The essence is to know most popular letters and become able to write and read original scripts :-)

Here I will post some really good websites that have great alphabet class.

http://www.southasia.sas.upenn.edu/tamil/tamilsound.html

https://en.m.wikipedia.org/wiki/Tamil_script