What is the ruling on returning to one's wife after three irrevocable divorces, especially after three years have passed, with children involved, and neither party has remarried?

If you divorce your wife three consecutive times with the intention of establishing the divorce, she becomes irrevocably divorced from you with a major separation (baynunah kubra), and she is not lawful for you until she marries someone else. If you intended to emphasize only the first utterance, then only one divorce takes effect. As for your statement, "You are forbidden to me until the Day of Judgment," if you intended divorce or ẓihār (a type of pronouncement of unlawfulness) and it was preceded by three or more divorces, then nothing is incumbent upon you. If you intended ẓihār, then the expiation for ẓihār is incumbent upon you. If you intended an oath (yamin) or did not intend anything, then the expiation for an oath is incumbent upon you.