Step one:
First draw an oval shape, pay attention to the sharper bottom.
Step 2:
Then draw several shapes of different sizes.
Step three:
Then use small polylines under each oval to draw its lower part.
Step 4:
Connect them with a few lines.
Step 5:
You can also draw a bow on the connected parts.
Step 6:
Finally, apply nice colors, and the colorful balloons are finished.