Why will children born during the millennium need to make a choice about God?
They inherit the same Adamic nature as their parents, so despite Christ's benevolent rule and the absence of satanic influence, they must personally exercise free will. To make a real choice possible, Satan is released for a little season to present an alternative and tempt them, as he did Eve.
Les explains that children born during the millennium come from believers and will have no opportunity for out-and-out rebellion because no satanic force is operating and Christ rules with absolute benevolent power as King. Nevertheless, they are born with the same old Adamic nature as their parents. At the end, Revelation says Satan must be released for a little season. Les says this whole new generation who never had to make a choice for or against God must be brought to a place of choosing; they must exercise free will even as everyone else did. A choice requires more than one option, so Satan returns for the sole purpose of giving these new generations that choice. He is given full opportunity to present his options, just as he did to Eve in the garden. Because the Kingdom has been so glorious, the temptation must be similar: Eve had it that good, yet Satan tempted her with “You can be like God.” Likewise, Satan will tempt the new generations with the concept that though they have it perfect, they are still not God.