This lesson is hands-on already; add a whole-body model of current flow so the "complete loop" idea is felt, not just built.
Be the circuit
Students form a human circuit: stand in a loop holding hands, with one student as the "cell" gently squeezing to send a "pulse" (a hand-squeeze) around the loop. One student is the "globe" who raises their free hand (lights up) each time the pulse passes. Break the loop — open a pair of hands — and the pulse stops: a switch. Students feel that the loop must be complete and unbroken for current to flow.
Build, break, fix
In the real circuit build, deliberately give some groups a broken component (a dead cell, a loose clip) and task them with finding and fixing the break by hand. Troubleshooting physically reinforces what a complete circuit needs.