Two points about assumptions made, which turn out to be unfounded, are that the Deuteronomy verse gives "the exact same phrase to describe those entering the Promised Land as used to warn Adam/Eve" and "about the tree that gives this knowledge." The verse in Deuteronomy reads,
"Moreover your little ones, which ye said should be a prey, and your
children, which in that day had no knowledge between good and evil,
they shall go in thither, and unto them will I give it, and they shall
possess it." A.V.
"And your infants, of whom ye have said, For a prey they are, and your
sons who have not known to-day good and evil, they go in thither, and
to them I give it, and they possess it" Y.L.T.
"That day" refers to the day the nation of Israel chose to reject the exhortation of Joshua and Caleb to enter into the Promised Land, to start taking it as the inheritance God had promised to them. They were on the border, 12 spies were sent out, but only two urged the people to trust the Lord's promise that that hill country of the Amorites would be conquered by them. Because of their disbelief, God was angry and said that not one person "of this evil generation" would see that land, bar the two faithful spies and their families.
As Moses reminded the nation of their disbelief, he then spoke what's written in verse 39. This shows that there is no direct connection between the phrase there, and the phrase in Genesis about a tree. Although it is called "the tree of the knowledge of good and evil", Deuteronomy speaks of little children too young to be included in the culpability of their parents' choice "that day". The parents deliberately chose an evil, disobedient course, and paid for it with their lives. Their little children were innocent of that, so God promised that they would enter the Promised Land, but not the older "evil generation" that had deliberately made a sinful choice.
The Hebrew word used in Deuteronomy 1:39 is 'yada' = 'to know', and is correctly translated as "had no knowledge between good and evil", unlike the parents whose disbelief of God on that day would rightly cause them to be labelled an "evil generation".
In Genesis something rather different is being unfolded. There was no law given by God to the couple in the garden. And it is only law that enables sin to be identified, exposed as sin, as evil, and requiring punishment. Romans 3:20 states, "For by the law is the knowledge of sin." Had the couple been given law, they would already have known about the evil of sin. They had been instructed in the form of a warning as to something that would cause them to die. Yet they chose to disbelieve God and decided to try something that held out a [vain] promise of elevating themselves to an even higher degree than God had created them as. They were already made in the image, likeness, of God. They knew nothing but good from God. Oh, but that wasn't good enough for them, once they believed the lie that they could choose for themselves how to aspire higher.
We all know that no fruit from any tree can impart knowledge, either of good, or of evil. The Genesis account teaches us higher things that require spiritual discernment. The first couple were culpable before God because they chose not to believe him. In Genesis 2:9 & 17 the Hebrew word for 'knowledge' is 'daath', which is not the same word as in Deuteronomy 1:39. Yes, the Deuteronomy account certainly reinforces God's warning to his people who think they can choose to disbelieve God's stated word and decide for themselves what they think will be the best course. But at a literal level, the children there had no knowledge of any of that and so they were not culpable before God on "that day". They would grow up and despite being sinners themselves, 40 years later they would take the Promised Land, having buried all of the previous "evil generation" in the wilderness. Not because they deserved to, but because God had promised that they would, and God never lies. God decided who would die in the wilderness, and which of their offspring would eventually enter it.
Conclusion Summary: So, it is not correct to assume that the Genesis and the Deuteronomy phrases about good and evil are the same. In Genesis, the couple thought they would learn about good and evil so as to put themselves on a par with their Creator. That sinful choice that day cost our first parents paradise, and cost them their physical lives many years later. As children of Adam and Eve, we also make sinful choices and "the wages of sin is death" (Romans 6:23). In Deuteronomy, the children remained innocent of the sinful choice their parents made that day, which gave those parents the label of "an evil generation" because they had God's law by then. Their choice cost every one of them their lives outside of the Promised Land before 40 years were up. There are intriguing lessons to be learned by comparing both accounts, especially the spiritual application.
Those who do not know good and evil are to enter into the land of promise. They are repentant, knowing that they do not enter in by their knowledge, nor by applying to law. They are humble because they know God decides who will enter, and who he will keep out. They enter in, following the Lamb wherever he goes.
