12 year old sex

My 12 year old sister is "in a relationship" and having sex with a 16 year old

Im shocked

I dont know what to do

I just i dont know i never thought this would happen!

Hes a sweet kid but I just cant look at him

She only told me because she thought she might be pregnant

(She hasnt even had her period yet so no chance of that thank god)

What the hell!

***UPDATE***

So i didnt tell my parents

But I spoke to the both of them

And by spoke I mean lost my mind

At first she had a little go at me because well she's 12 and 12 year old knows everything

But then I seperated them and explainrd to him very nicely how if he ever came near my little sister again I would be turning him into the cops because i found texts on her phone with very disgustingly explicit messages (i felt bad snooping but i felt it was necessary)

He pretty much shit his pants at the thought of his parents finding out and was legitimately crying which made me happy

He deleted her from his phone in front of me and promised he would never speak to her again which i hope for his sake he doesnt

Then I went and spoke to my sister and had a very deep and personal conversation with her about it which involved her crying alot which broke my heart

She didn't even know what she was doing for the most of it and was shattered over what had happened

She explained how she met him in their study group for all aged students at their school, we're going in on monday to ask that she is moved to another one, im hoping that they will let her do it and if not ill explain why and just pray they dont tell our parents because she is scared they will disown her because of it, i told her thats not the case but shes terrified

Thank you to everyone who was supportive throughout this

I wish I could go to the cops about this (and probably still could) but my sister just wants to move on

Shes a smart kid, just a low self esteem

Im still shocked that this happened at all