The key part of that phrase is "And knew her not till she had brought forth her firstborn son: and he called his name JESUS -Matthew 1:25 " The clear meaning of this scripture speaks for itself. Anyone that believes that Mary and Joseph somehow remained celibate for years and years have the burden of proof (not the other way around). In fact we are explictly warned not to make up scripture.Exactly...That is the definitive statement...It couldn't be more clear...
After Jesus was born, he KNEW HER for the first of many times...