Why not, as a defender, just walk around it, into the BC, and take the ball (if on the floor)? I realize that it is not allowed but who cares? The ref will stop the game and the defense will get what they accomplished. Yes, they could then inbound in the BC and do the same thing but come on, these are 11 year olds. What kind of coach teaches this to 11 year olds? Yikes.
How could 4 11-year-old girls occupy the entire half circle perimeter without being in an illegal position. If feet are greater than should width apart, in order to accomplish this, call an illegal screen, lol. Or, if that far apart, crawl through the legs. When the defender collapses them, call a foul on her, lol.
I do believe that locking arms/hands is illegal.
I would use a T as an absolute last resort in a game involving 11 year olds.