Charlie's normal reaction to these things is to charge out and see what's going on, but not this time. This time he's taking his son to one of the upper floors (just in case it is like the time the monsters came, rising up out of the ground). Then of course, not wanting his son to get sick, he'd do all the warming charms and swaddles he knows to make sure he stays warm enough. Then he'd probably go about warding the place up even more than it normally is. Like, we're talking magical barriers in every doorway/window, especially in the rooms leading towards Alexander.
Then Charlie will probably go sit near the front window and watch for anything that might try coming into the house. He's getting even less sleep than usual.