Does anyone think i am wrong?

i wont let my son over his grandmas house alone because she belives in him when he does something wrong. i think is a terrible thing to do to a child my mom ed and abused me very badly when i was younger and it has messed me up for life i still havent forgave her for it but i let her see her grandson as long as im there when i was younger i was beat with metal broom handles gave me bloody noses just cuz i didnt clean the house fast enough or just cuz she had a bad day it happended till i was 17 till i finally ran away. i dont want my son to go through that ever am i wrong?