"It's quite all right if your father shows you around the public areas of the house." This will be understood, he thinks, to mean that other people's bedrooms are off-limits, along with locked areas. "However, you shouldn't wander unaccompanied. Your father, or Miss Saint Croix, or Mr. Lyall must be with you at all times, or Lord and Lady Valdemar will be displeased." More to the point, it seems more than plausible that a child, particularly one of an age to still be in the nursery, would be capable of unintentionally disrupting any number of experiments, destroying valuable books, and so on.

He offers the lemon drop again. "Take it." His attempt at a small, encouraging smile doesn't quite make it to his eyes... but then, it rarely does. He's rarely an indulgent man.