My earliest dream was when I was 3 years old, there was a basketball court across the street. The goals were raised on horizontal poles that were curved to connect to the concrete, so you could swing under them. One day my sisters (ages 4 and 5) and I were swinging under them and my older sister leaned her head to far back and hit her head on the concrete. The back of her head was bleeding, but she wasn't crying she just put her hand to her head with blood dripping on the ground and walked inside the house and up to the second floor bathroom. My oldest sister was hysterical and incoherently explaining what had happened to our parents, who had seen the drops of blood. I then walked in calmly after checking on my bleeding sister and explained what had occurred and where she was in the house. To this day I've retained my ability to stay calm and manage emergency situations when others are frantic.
This memory stands out to me due to it being a traumatic scene, especially to a young child. Watching a loved one have their head cracked open on concrete is gory and scary, but I remained calm enough to make the accident clear to my parents.