Periscope from a paper-towel tube

Hand the child a paper-towel tube.

Hold the tube up to your eye. Look through it. Slowly pan around. "I see a chair. I see a lamp. I see you."

A 4-year-old will spy on everything from behind couch cushions. The narrow field of view changes the quality of looking — they notice details they normally miss.

Bend the tube (use two tubes taped at right angle) for a real periscope feel — works for looking around corners. Add a "spy list" — find five round things, three blue things.