Lost birthday

I was talking to a Khmer girl about my age and she said she didn't know when her birthday really is. Kimsoeun doesn't know what day he was born on- it was some time during Pol Pot time so I don't think his mum knew what day it was. But I was surprised that my friend didn't know. She said her mum had heaps of kids and didn't keep track. I guess in Australia you must register births with the government, I think you can do that here to, but you don't need to do it right away. Both my friend and Kimsoeun made up their own birthday when they started going to school.