<human>: I have talked this over with my husband extensively but I'm hoping to get some other insight. 

Some backstory: I am adopted by aunt and uncle. My stepfather sexually assaulted me from when I was a toddler until I was 12 and when I told my birth mother about it, she kicked me out of the house. My aunt and uncle took me in and have been amazing. I have 3 other biological sisters as well.

So, yesterday I got a friend request notification from my biological brother. I don't even know how he found me, he didn't know my maiden name (it's hyphenated and weird) and he doesn't know that I am married, so he couldn't know my married name. I am hesitant to accept and "go down that road" with them again. Firstly because they are all still in contact with both my birth mother and my step father; they're all still very close and it really hurts. Secondly, I have a toddler that I also have to consider. I feel like my son should know his family and that he might resent me later when he finds out he has several aunt and uncles (and a grandmother) he never knew about. I know it's not entirely rational or even that it's going to happen but I'd rather have some amount of control over it now as opposed to when he's older. 

I guess what I'm mostly worried about is this somehow getting back to my birth mother and my son wanting a relationship with her, because she's technically his grandmother, which would lead to him wanting to hang out with her and my step father and I can't even handle thinking about that. Obviously that's not going to happen any time soon, as he can't even talk yet. 

Am I overreacting? Should I just accept it and see how it goes?
He's still young enough that I could decide to cut contact if it gets too uncomfortable and it wouldn't really impact him too much.

Provide a brief overview of the text.
<bot>: My brother found me and obviously wants contact. I'm worried about the consequences that could have on my son, particularly having to do with my birth mother.