First off, good job with the refined illustration! I just noticed after looking at the image a second time that you added the detail of the stuffed Koala bear, which is a great emotional link between the first image and the third.
To answer your question about suspense, maybe consider having the dog barking? Not like an angry bark but a "Hey human, there's something out there!" kind of bark. That way it answers the question of 'why is the boy awake?'.
I also like the colour choice of yellow light, with cooler shadows, though would suggest changing the colour of the action figure in the top left corner to a cooler colour. This is to keep focus directed more to the boy and the dog. And I realize that realistically the figure would be lit the way you have it, and toys are usually be coloured with bright colours like reds and oranges, but hey, we're the illustrators and we can fudge reality a bit if we want to
But in all, it's a cool short story, and could probably turn into a bigger project if you wanted to!