Pull cushions off the couch. Lean them against each other to make a small enclosed space. Leave one small gap — the peephole.
Crawl inside. Peek out through the peephole. "Hello!"
Total immersion. Kids will spend an hour in a cushion fort and play seven different pretend games inside it. The "world out there, me in here" is half the appeal.
Add a blanket roof. Two forts that connect via "tunnel" (a gap between cushions). Snack inside the fort.