Do i have cause to worry igo out for an hour in the evening & come home to find my 2yr old not there?

You need to lay the law down. He is your son and it is up to you what the limits you set for him are. With that said you do live with your parents and that always makes it harder to set limits. If it was me I would quit leaving him with them unless I had to go to work and couldn't find alternate childcare. Then you don't have to worry about them watching him and doing things you don't agree with. I would feel the same way about my child walking around at night. Too many bad things happen. Good luck!