Why didn't the entire village know Naruto was Minato's son?

Question

Besides the out of universe reason that his identity was hidden as a plot device, is there any in universe reason people don't know Naruto is the 4th Hokage's son?

After all, Minato was married to Uzumaki Kushina. She must have been pregnant for a while before her and Minato's death. Being the wife of the 4th Hokage, she must have been, at least to some degree, a celebrity figure. Everybody would have known she was pregnant. She must have been sporting a good baby bump for at least a couple months before her death. Shortly after the time of her death, there's suddenly a newborn baby named Uzumaki Naruto wandering around (that happens to have a striking resemblance to the 4th, which becomes more and more obvious as he ages), and nobody made the connection they were related?

Suddenly orphaned, Naruto was left to grow up knowing nothing of his parents, receiving only his mother's last name because the Third Hokage thought that it was best that nobody knew that he was related to the Fourth Hokage.

I know that the Third hid his relation to the 4th, but simply using the 4th's wife's last name doesn't seem like it would be very effective. Was that really all it took to fool just about EVERYBODY? Is there some other explaination to Naruto's anonymity?

Answer 1

While I don't like posting speculative answers, upon plenty of time and thought I think this is the best I can think of. Expanding on my comment on the question, I'll try to logically conclude why many didn't relate the boy Naruto with the son of Hokage.

1. We see the scale of invasion pretty early in the episode and see it was a sudden war worse than the attack by the Sand/Sound villages. The strategy of saving the villagers probably resulted from the Nine-Tailed Fox Attack. The knowledge of Jinchuriki is SECRET information and wasn't revealed to anyone but the Hokage and top-tier Anbu. Hence, while plenty of people had seen Kushina pregnant, no one knew the significance of the birth (even Minato didn't know). The sudden death of the Fourth and his wife naturally led people to conclude the worst. We also know that some Anbu and the Third's wife died as well. When so many people die together, how can they assume a new born baby survive?
2. We know of at least two orphans from the Nine-Tailed attack. Iruka and Naruto. (I believe Kurenai's parents died too, but not sure if it was filler). When the Third Hokage retook the position, the village was turmoil, and plenty of rehab efforts were made, including for orphan children whose parents had died. Uzumaki Village is extinct, but there may have been several wandering clans in the Land of Fire (not the village), who may have visited the village. And Naruto may've been thought to be the son of guests who unfortunately died in the attack. The nature of the Third's kindness is well known and no one would question his interest in the kid of a guest of the village who died because of the failure.
3. The Hokage's family are treated as special in village. Tsunade (the First's granddaughter), Asuma (ran away from home to escape the shadow of Hokage's son), Konohamaru (Honorable Grandson + Special Tutor) and even Boruto (Konohamaru would naturally take him in). Everyone likes them. Treats them with respect. In Naruto's case only the shadow of fear lingered, and it didn't change. If he were "special" why didn't anybody intervene? This created the vicious circle of some people staying away because of the fear that being the Fourth's son makes him a target (Kakashi), some jounin let him be (Shikaku), some actively shunned him. This shunning gradually increased and seeped into the kids as well. No one expects a village oddball to be that of Hokage heritage.
4. The most important point is hiding in plain sight. Naruto isn't the first nor the last to use this technique for hiding the true nature of main character. Superman is a prime example. People don't expect "special" people to live among the common! What they don't expect they just don't see it. This is true in real life as well.

Answer 2

It's because Minato stated when Naruto met him first, that if anyone knew that Naruto was his son, then he'd be in danger.

Answer 3

So I read on naruto.fandom.com that Kushina’s pregnancy was actually kept in secrecy from the general public. So even though no other child in the village has striking yellow hair, like the fourth, except naruto, there technically still isn’t a reason to relate him to the fourth because no one of the general population would have a reason to speculate that the fourth had a child. I also read that Kushina was to be the next jinchiriki of her generation because she had special chakra.So she was sent from the Uzumaki clan to Konoha and enrolled in the school. And since everyone knew that naruto was the jinchuriki I’d assume that everyone knew that Kushina Uzumaki was also the jinchuriki of her generation. It’s also important to note that another Uzumaki possessed the nine tails before Kushina, so when an orphaned kid (after the war when there are many orphans) of the Uzumaki clan shows up who possesses the nine tails, it’s not really a big whoop and certainly no need to make a connection that the kid may belong to the fourth and his wife Kushina even though he has yellow hair and is an Uzumaki. No one knew the fourth and his wife were expecting a child and when Kushina Uzumaki died they just put the demon in another Uzumaki keeping the trend going for the third generation of the Uzumaki clan.