For around 8 years, cause that's how old these shins should be no one detected them.
Naruto showed some amazing sensor skills in both Sage and Kurama mode, he entered them both countless times during these past 8 years probably, even if just for fun (as mentioned with Boruto, when they were playing hide and seek).
Also, Sasuke was out in the world, tracking for Kaguya's chakra, for the past 7 or 8 years as well, and he didn't notice around 100 mutant kids that have some malefic chakra.
Not only these 2, if you remember the Sensory unit that was during the war, I guess their children have taken over, and should be doing something similar to their parents' doing.
The biggest flaw is probably Naruto not sensing these with KM, when he was able to sense Shikamaru, Neji and Kiba inside that barrier, when they should've been practically sealed off totally. Yet, he had no idea that these people exist.
And also the other 2 that I've mentioned.
Naruto showed some amazing sensor skills in both Sage and Kurama mode, he entered them both countless times during these past 8 years probably, even if just for fun (as mentioned with Boruto, when they were playing hide and seek).
Also, Sasuke was out in the world, tracking for Kaguya's chakra, for the past 7 or 8 years as well, and he didn't notice around 100 mutant kids that have some malefic chakra.
Not only these 2, if you remember the Sensory unit that was during the war, I guess their children have taken over, and should be doing something similar to their parents' doing.
The biggest flaw is probably Naruto not sensing these with KM, when he was able to sense Shikamaru, Neji and Kiba inside that barrier, when they should've been practically sealed off totally. Yet, he had no idea that these people exist.
And also the other 2 that I've mentioned.