I believe the argument started with the decline of Christianity. This decline is happening mainly because of older Christian’s are dying and there children are not continuing the faith so in a sense those younger children never truly embraced Christian ideals. You have to wonder however why so many millennials did not do so.
No it doesn’t mean they weren’t Christian to begin with it says they have turned away from God not that they never were with him Judas was with Jesus and followed his teaching but still betrayed him he’s a great example of someone who was given the proof to believe yet still turned I. The son of God for 30 silver shillings