What is the best initial action in response to a child who has experienced significant bleeding from a wound?

Applying pressure to the wound with gauze is the best initial action when a child has experienced significant bleeding. This action is crucial because it helps to control the bleeding by promoting clot formation and restricting blood flow from the damaged blood vessels. When direct pressure is applied to the wound, it can significantly reduce the amount of blood lost and help stabilize the child's condition until further medical help can be provided.

The other options do not effectively address the immediate need to control bleeding. Waiting for the child's parent to arrive does not provide any immediate intervention and could lead to further complications from blood loss. Leaving the wound uncovered can exacerbate bleeding and increase the risk of infection. Providing water to the child is not relevant to managing bleeding and could be dangerous if the child needs medical attention. Immediate and appropriate action is essential in emergency situations to ensure the best possible outcome.