Final answer:
John Clark's statement that Will is too young supports the inference that he wants to protect Will by keeping the mission a secret to shield him from danger.
Step-by-step explanation:
The detail from “A Ride in the Night” that best supports the inference that Will’s father wants to protect his son by keeping the mission a secret is “He looked hard at Will. ‘Yes, he’s too young,’ John Clark agreed.” This statement indicates that John Clark, presumably Will’s father, acknowledges the risks involved and possibly wants to shelter Will from the danger by agreeing with the sentiment that Will is too young for such serious matters. By doing so, he could be trying to keep Will at a distance from the dangers of the mission, thus protecting him.