Never leave a window unattended, especially when children are present. Falls may result in serious injury or death. If you do find streaks, you'll know which side needs to be redone. Change the water often to limit or eliminate streaking. Letting the solution dry onto the window while you climb up and down to retrieve your tools could be the difference between sparkle and debacle.
Sunlight dries the solution too fast and makes streaks more likely.
Hard water stains can be stubborn. All trademarks or product names mentioned herein are the property of their respective owners.