Ill answer to the guestion: "how do they know they are crystal/indigo child?" and "how do you tell if you're an indigo/crystal child?"
first off (I dont really like to be mentioning it but..)
I'm a crystal "child", well not a child anymore, but I once was a child.
I have never knew the term "crystal child" when I was little,
I just knew I was different, and people really didnt understand my thoghts well. I think my grand parents know the fact actually, but they havent told me - they just treat me like it (my grand father was able to see auras, but he doesnt live anymore)
I have got to known my problems and what I can do.
The way I got to know why I am a crystal child is:
1. all the descriptions fits on me
2. I have that kind of aura they have
its like "knowing how to play some game without knowing its name."
there is no way I can actually tell it, I can never prove it to you - if you cant see auras from disrtance or something, you can just see what kind of person I am here and decide to trust or not.
thats the why I dont really like to tell I am crystal, because there is no way of proving it really. Only my closest friends have known it since now. now everyone knows who reads this - but oh well, most inportant was to answer the question.
ofcourse the best way is to show ones aura to the certain person who wants the proof.