Batman followed the boy around, his eyes narrowing when he saw the gun picked up and the sword drawn. It was time to intervene.
He considered his next few moves carefully, judging the distance between the boy and the guard at the front of the building. There was enough room still that they could speak softly and not be overheard. Rappelling down from the roof he landed quietly behind the body and reeled in his line, replacing it on his belt before speaking, his voice pitched low.
"Put it away before I take it away."
He had no fear of the boy turning and striking him. Batman had trained enough with the League that he knew he could either counter or get out of the way of any attack made should the boy be unable to check his reflexes.
"Give me the gun," he added. Batman was counting on the fact that the boy knew who he was and, as he'd been looking for him, might actually do as he said without argument.