You might explain to them that it is a common misconception that the term "antichrist" in the Scriptures refers to a single individual. There is actually no such individual named or foretold in Scripture, but rather there were "many antichrists" who had come already in the first century. In fact, the apostle John cited this fact as the reason he knew with absolute certainty that it was the last hour. The reason he knew this is that Jesus had told him what signs to look for. In addition to the many "antichrists" that had come already back then, the Bible also speaks of a "spirit of antichrist," which is a lying spirit that denies Jesus is the Christ (cf. 1 John 2:22). These "spirits of antichrist" will always be in the world. But the "many antichrists" of whom Jesus and the apostles spoke are limited to a specific time period, during which Jesus predicted that all which had been written of him in the Scriptures would be fulfilled.
While eschatology is not the focus of this exegetical essay on 1 John 4:7-21, the eschatolgical *context* of the passage (including John's reference to the "many antichrists" which had already come) is strongly emphasized:
Because He First Loved Us:
An Exegesis of 1 John 4:7-21 within the Context of 1 John