What is n "Open House" then? Is there no structure and no interaction/meetings with faculty and current grad students? Is it literally just a day where you come walk around the buildings?
I literally just made an account moments ago just to tell you that this would be incredibly weird. Do not bring your mother. Nobody else will have parents (or friends) there. You are an adult and this will make you seem like an immature child. I don't know of any program/circumstance in which it would be normal to bring a parent.