(Amplified Bible:)
1 Corinthians 7:14 For the unbelieving husband is set apart (separated, withdrawn from heathen contamination, and affiliated with the Christian people) by union with his consecrated (set-apart) wife, and the unbelieving wife is set apart and separated through union with her consecrated husband. Otherwise your children would be unclean (unblessed heathen, outside the Christian covenant), but as it is they are prepared for God [pure and clean].
IMHO, only children who have at least one saved parent (better that both parents be saved) go to heaven if they die before the “age of accountability”.
1 Corinthians 7:14 - I concur with your interpretation. Thanks for finding that scripture, I had forgotten it.