Final answer:
The best action after ensuring the child's ABC's is contact medical control for proper guidance, as administering substances without medical advice can be harmful.
Step-by-step explanation:
Upon assessing ABC's (Airway, Breathing, and Circulation) and beginning transport to a medical facility, the next course of action for a child who has ingested an unknown fluid with signs such as reddish mouth and lips, along with coughing and gagging, would be (d) Contact medical control for direction. Administrating substances like syrup of ipecac or activated charcoal should not be done without specific instruction from a poison control center or a physician, as they can be contraindicated in certain situations. Seeking medical advice is crucial to ensure the child receives appropriate care and any potential complications or interactions with the unknown substance are adequately managed.