Final answer:
The quickest and best way to establish vascular access in a child with hypovolemic shock is through the intravenous (IV) route.
Step-by-step explanation:
In a child with serious signs and symptoms of hypovolemic shock, the quickest and best way to establish vascular access is via the intravenous (IV) route. Hypovolemic shock in children can occur due to fluid losses from severe vomiting or diarrhea, extensive burns, exposure to certain toxins, and excessive urine loss from conditions like diabetes insipidus or ketoacidosis. Establishing an IV line allows for rapid administration of intravenous fluids and medications to restore normal function and raise blood pressure in an emergency.