on Original Sin

I've been noticing verses that don't seem to match up with my own understanding of original sin (note: either my understanding or the tradition itself might be off). Check these out:

Deu 1:39

Moreover your little ones, who you said would become a prey, and your children, who this day have no knowledge of good or evil, shall go in there, and to them I will give it, and they shall possess it.

Isa 7:16

For before the child knows how to refuse the evil and choose the good, the land before whose two kings you are in dread will be deserted.

Heb 5:14

But solid food is for the mature, for those who have their faculties trained by practice to distinguish good from evil.

Each of these suggest that discernment between good an evil (a la Gen 2:17) does not exist before some development of maturity.

Ps 51:5, on the other hand, seems to suggest that we're born in a state of sin.

Behold, I was brought forth in iniquity, and in sin did my mother conceive me.

Now the traditional solution (I think) is to say that sin doesn't depend on awareness. However, as the Deuteronomy passage describes, it seems like the effects of sin do. The children of Israel (who don't know 'good or evil') are allowed to enter the land even though the adults may not.