When Tommy says, “They sent four people. A mother and a father and two kids who looked just like humans... but they weren't," what is the effect on the crowd? The monsters are due on maple street

The effect on the crowd is one of fear and suspicion. The mention of a seemingly normal family who are actually not human adds an unsettling element to the situation, causing the people on Maple Street to become even more paranoid and wary of each other. This revelation heightens their anxiety and fuels their growing sense of paranoia and distrust towards their neighbors.