When a couple marries in the Church their sincerity is assumed. They may have sexual relations, and any children resulting from those relations are legitimate because their sexual relations are legitimate. If it is later discovered that there was no true marriage, that does not mean they committed any sin.
Wait just a tick.
If the marriage wasn’t legitimate how could the sex that took place possibly be legitimate? Isn’t sex outside of a true marriage a sin?
I know you are writing in English, but the way you strung the words together makes absolutely no sense whatsoever.
“If it is later discovered that there was no true marriage”
You can’t later “discover” anything, since the annulment is based on what your or your spouses’ thoughts and motives were at the time you were married. I suppose one spouse can discover it, but it Takes Two To Tango, so to speak...