Anchorhead said:
Indy and Marion clearly had a past that was bordering on inappropriate. Marion mentions it directly; "I was a child. It was wrong and you knew it".
I've never taken that so literally. When she says she was a child, I've always felt she meant she was young but not school-age young. Same with Vader referring to Luke as "just a boy" even though he was in his twenties by that point.
I think Lucas is deep, but just not as ebullient as some directors.