The nature of the charges present on the surface of the charged balloon is same, Since the like charges repel each other. Therefore the two charged balloons repel each other. As shown in the figure below.

When the charged balloon is brought near the uncharged balloon, the uncharged balloon acquires the charge opposite to the charge of charged balloon and we know that unlike charges repel each other. Therefore the uncharged balloon is attracted by a charged balloon. As shown in the figure below.