Why no current in neutral wire_kids question
... then why there is no current in the neutral wire?


Yes, Virginia, there is a current.1.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. The building supply comes from the utility company's transformer. One of the transformer outputs is connected to earth and so is "neutralized.

Current must return to the source as you suspect. The pupil may be getting confused with voltage and since the neutral wire is connected to earth there is, nominally, no voltage on the neutral wire with respect to earth. In practice the neutral wire has some resistance so a voltage proportional to the current (V = IR, Ohm's Law) will appear at the lower terminal of the lamp. This shouldn't be more than a couple of volts in normal operation.