After the Israelites crossed the Jordan but prior to invading Jericho, the LORD told Joshua:
"Make flint knives and circumcise this second generation of Israelites." (Josh 5:2)
Josh 5:5 stated that the first generation out of Egypt were already circumcised, which is understandable since it was a mark of the Abrahamic covenant (Gen 17:9-14). The command to circumcise was also given to Moses in Lev 12:3:
On the eighth day the boy’s foreskin must be circumcised.
which renewed the instruction given to Abraham in Gen 17:12:
From generation to generation, every male child must be circumcised on the eighth day after his birth...
It's interesting that the narrator of the Pentateuch never mentioned this failure negatively although the penalty was serious:
Any male who fails to be circumcised will be cut off from the covenant family for breaking the covenant (Gen 17:14)
and there was even an incident that the LORD almost killed Moses for failing to circumcise his son (Ex 4:24-26). See a gotquestions.org article for a typical interpretation.
Several related factors:
If we read carefully the 2 most serious incidents where the LORD Himself almost took them "out" of the covenant by re-establishing the chosen people under Moses's descendants (Ex 32:10, Num 14:12), the LORD later relented after Moses's intercession (Ex 32:14, Num 14:20).
From the 1st gen's side, there was fear, distrust and wanting to do their own way, but they never explicitly rejected the Abrahamic (and possibly the Mosaic) covenant (or did they?). The distrust didn't seem permanent because they did repent (Ex 33:4, Num 14:40b), implying that they wanted to be back in covenant although the 2nd time around (the spy incident) God decided to deny the 1st gen. entrance while they raised their 2nd generation in the wilderness. Similarly, in the NT, a non-permanent fear, rebellion, and distrust doesn't mean we are out of the covenant because of God's faithfulness to accept us back as long as we repent.
From the LORD's side, He continued to show His faithfulness to the covenant to the 2nd generation by a) continuing the journey after the Golden Calf incident (Ex 32) until just before the spy incident (Num 13-14) and b) explicit affirmation that the 2nd gen will enter the promised land (Num 14:31).
The Narrator never indicated explicitly that the Abrahamic / Mosaic covenant was broken prior to the 40 year wandering, but that the 1st generation was simply punished.
On the other hand, failing to circumcise is more serious than temporary distrust because "any male who fails to be circumcised will be cut off from the covenant family for breaking the covenant." (Gen 17:14)
Therefore, at the start of the 40 year wandering (just after Num 14), while it was clear that the 1st gen would die in the wilderness (as punishment), it seemed clear that the covenant was intact, at least for the 2nd generation. If I were a parent of the 2nd generation, the very least I would do is to make sure that my kids are "in" the Abrahamic covenant by circumcising them on the 8th day even though I myself was denied covenant benefit.
Thus the question remains: after the spy incident, during the 40 year wandering in the wilderness, knowing that God promised the 2nd generation to enter the land (Num 14:31), why Moses didn't say or do anything to make sure that the 2nd generation was in the Abrahamic covenant given that 1) he wrote Gen 17:14 and Lev 12:3) and 2) the LORD almost killed him for failing to circumcise his own son (Ex 4:24-26)? But most interestingly: why the LORD wasn't angry at this failure, or why the narrator of the Pentateuch didn't say anything negatively about it?