i can give yah all the insight i know on them from personal experience because i myself am technically one but am not one anymore. first off the easiest way you can tell who an indigo child is is from there aura,people say that an indigo child's aura is indigo(self explanatory), but i have found that a lot of indigo children possess colors like blue auras, purple , bluish indigo, red indigo , and violet.
now let me tell you more things that normally do with indigos. indigos normally exhibit signs of a.d.d and a.d.h.d at young ages(people will tell you this is bad and try to clog the child with medication). i was one of those children, i would star out the window all day thinking of things like world peace, and how tall ill be when I'm older. another sign of an indigo child is that they seem to be different in good and sometimes weird ways. they sometimes feel lonely and unaccomplished because they feel as though no one understands them, but get a group of indigos in a room and they will hit it off.
now lets talk about the spiritual side of a indigo. indigo children seem to have heightened esp(extra sensory perception) a lot of indigos exhibit lucid dreams, cognition dream, the ability to see auras with ease, and many many more things.personally as a child i couldn't see auras but i could feel auras really well and still can. all my life I've always had excellent feelings on who to be friends with and who to stay away from.
lastly how i found out i was an indigo at one point. before i knew what the word was i knew what auras where and i knew my mother could see them damn well. i was around 12 years of age when i asked my mom to see my aura. she told me the color she saw was something that looked like a weird blue. so i looked up on google a bunch of colors that resembled blue, baby blue light blue, powder blue, just a bunch . when we finally came across the color she said it was indigo. at the time i thought nothing of this but i just thought cool thats a nice color. years later when i was 15 i found out about indigo children. i read all i could about them and i was amazed every single thing describing them was me, the thing that astonished me the most was the add things. so when i was done reading all i could on the matter i asked my mom to see it again, and she said it was indigo with a slight purple above.over years it became fully purple then purple with violet, then white when i hit about 17. and now to this day its a bright white with yellow ontop. which brings me to another topic on its own but relates to indigo children. and thats crystal children.
p.s i hope this helped you , i might be leaving out stuff about indigos but this is just a rough sum up of it.