My sister is crying what should I do?

Ask her what's wrong.

Maybe she is hungry or want to go to the toilet~~

try to make her feel better, give her some water to help make her calm, and some tissues, and ask her whats wrong

Ask_Sean Says, Comfront her and ask whats wrong like any other person would do?

you could tell her that she means the world to you.

If you are her sister and you know that you don''t spend much time with her/him then take them somewhere in the house quiet, then find either make a hot chocolate or have some cake and talk with her. Have a good long talk with her. Then maybe you can watch a movie together and just enjoy eachothers company!!!!

you could spend a day with her/him. Dedicate it to her/him. She/he is one of the most important things in this world. And life doesnt go on forever.

I LOVE JUSTIN BIEBER!<3