Grounding can mean what you make it mean in your home.I would base it on what the offense had been.
If I wanted to grounding him at the age of 6, it would have been no TV, video games all weekend. And no going to anyone's house if invited, and canceling any play dates that had been planned during the grounded time.
I would have continued to do my own plans for that weekend, but if I was busy, your child would have to entertain himself. He could read books or play quietly in his room. He would have to continue to run my errands with me and help with his typical chores. And better be on his best behaviors.
Stick with it. At some point, speak with him about how you are disappointed in his behavior.
Remind him why he is grounded. When he speaks about being "someone else fault", do not allow him to continue..
Tell him it is only his fault. He is old enough to know not to break your rules. He could have come back into the house when (if) someone was trying to get him to break the rules.
I remember my mom saying, if "Suzy" is trying to get you into trouble, maybe you should not ever be allowed to play with her again. Do I need to speak with her about making you break my rules?" Of course I was mortified at the thought of my mom getting after someone else for my problems..
If he complains or gets sulky, remind him all of this is because of HIS behaviors. That you also do not appreciate feeling like you are also grounded, because you have to watch him in the house all weekend, and you had hoped to go swimming this weekend or the movies. or whatever you all had planned.
The most important part of a grounding is never going back on the promise that he is grounded. This way if you tell him, Do you remember when you were grounded for not following the rules? do you want to be grounded again? he KNOWS, mom is serious..