John laughed softly, quite aware of the slight blush in his cheeks. It was flattering, certainly, although perhaps rather unexpected.
"Are you calling me easy, now?" he joked, trying for self-confident, but perhaps falling slightly short of that. He cleared his throat; maybe comedy wasn't his strong point. "Heh, well, it's just a cold. Bring me the bubonic plague or something, and you might see a bit more panic," he smiled. "That's not a challenge, by the way," he added hastily. It was a worry, thinking about where the train was capable of taking them. Then again, it had always protected them from local disease in the past, by way of vaccination for example.
"Oh, not so long. A week or so," he responded. "If he's not on the mend after a week, bring him back along. Or if he gets any worse, of course," John told him, mixing together a solution of paracetamol into a syringe. He inserted it into the baby's mouth, waiting for him to latch on, and slowly squirted in into his mouth. "I'll make you up some to take away with you. At least four hours between doses, no more than four a day," he told him, managing to regain some professionalism.