Final answer:
Before hydrotherapy begins for a child with a full-thickness burn, the nurse should prioritize implementing pain control measures.
Step-by-step explanation:
Before hydrotherapy begins for a child with a full-thickness burn, the nurse should prioritize implementing pain control measures. Pain management is crucial to ensure the child's comfort during the procedure. This can include providing pharmacological interventions such as analgesics or topical pain relief measures such as cool compresses. In addition to pain control, it is also important to ensure that the child is adequately hydrated. However, administering fluids as ordered is not the immediate priority before hydrotherapy.