What is the caste of an illegitimate child

I am 37 years old man,born to a tribal women(ST).I never knew who my father is.My mother a government employee bought me up in tribal society,even i got married to a schedule tribe women.I want to be known by my mother's surname because at present i dont have any certificate to be known as ST.My mother and wife both are an ST women,i don't know what my child will be known as....please help....