To me, "that I used to play when a was a child." would do.
...idea of throwing objects into people who were passing below the balcony (or "below it").
No good to say it wasn't my idea.
It was no use saying it wasn´t my idea. OR
I said it wasn´t my idea, but it was no use.
I had to stay a week without TV and videogame.
I was ground for a week without any TV or videogames.
(Here just another way to say the same thing, I thought you should find it interesting to know. Not a correction at all, okay? it should keep it as it is.)