It is believed that on Christ’s return with His angels at the second coming, He will judge all nations (The sheep and goat judgement – Matthew 25:31-46) after which the 1000 year reign begins. Satan is said to be captured through this period but must be released after The Millennium to once again deceive many. Who are those to be deceived by Satan after the Millennium?
Everyone welcomed into the Millennial Kingdom from the Sheep and Goat judgment will be a believer (Matt. 25:34) and will still be in their natural state. As such they will have children who will also have children, etc. All children born during the Millennium will have to make the same decision about salvation that people make now. Some will choose to allow the Lord’s death to pay for their sins and others won’t. Those who reject the Lord’s death on their behalf will be the ones Satan deceives.