Teach them to read and to count (but do this gently - not every child can do this at the age of 3 easily and you should not force them). I was once surprised to

Teach them to read and to count (but do this gently - not every child can do this at the age of 3 easily and you should not force them). I was once surprised to know how many kids can't read at count as their parents don't teach them. Also introduce them to a foreign language.