The sudden realization of a quiet house with toddlers and preschool (when it is not nap time) can be terrifying because the possibilities of what they're doing is endless. As they get older, and less likely to get themselves in precarious situations, still question the quiet. Especially as they enter the tween/teen years. Be curious about what is going on in their thoughts. Be curious about their day. Be curious about how they feel. Help them continue to engage with you as their parent and the rest of the family if you notice it tapering off quite a bit. Family meal times can be a one way to do this daily.