The scene in the grain bin when the kids are sinking into the corn is way off the mark. And while that is a danger (usually fatal), the only way a person sinks like that is when the grain is being removed from the bottom of the bin. That's when a person is drawn down and suffocated. If the grain is stationary, there is no danger of sinking like that.
Taking blood pressure measurements during pregnancy is very important and its inclusion in the film was a good detail. However, when Blunt's character is taking her blood pressure, the blood pressure cuff is too low on her arm and she is not using the stethoscope to record the pressure. Given that using the stethoscope greatly improves the accuracy and makes taking the measurement easier, there was no reason that she should not have used the stethoscope.
Lee takes his son to the waterfall to note that loud natural sounds can mask their noises, with both yelling to demonstrate. If Evelyn was so far along in her pregnancy he should have set up some kind of camp there so that any screams from the childbirth could be masked. However, it's not very practical - or safe - for the family to be living outdoors day and night in this situation.
A normal indoor conversation at a volume of 66dB would have a noise level of only 39dB at even 20m distance - close to the normal environmental sound level of a forest (~40dB). With massive dampening from walls and soil in the line of sound travel would mean that any conversation would either be inaudible or at least masked by environmental noise levels. However, as seen in the film, the creatures have actually come right upto the house on occasion. The house is not made of bricks and the family obviously were being cautious incase one of them was right outside. Psychologically, it would make sense that a family in this unique and extremely traumatic situation would probably be overly cautious.
One of the newspaper headlines on a table is dated in mid-October 2018. Later in the film, on Day 473, the mother is writing on an October calendar as she keeps track of her pregnancy vitals. Assuming Day Zero was near mid-October 2018, then Day 473 should have been in late January or early February 2020. However, that assumption is clearly wrong as the little boy was killed in 2020 (as per the cross where it happened) which was Day 89, so Day Zero was obviously not in 2018. The days may actually refer to the number of days the family has been fending for themselves rather than when the aliens first arrived.
While pregnant, Evelyn uses a stethoscope to listen to the baby's heart in the womb. This may be difficult with a regular stethoscope but not impossible. There is a specialized type of stethoscope called a fetoscope which is simply a different shaped stethoscope but functions similarly. A doppler is more commonly used in today's hospitals to hear the fetus' heartbeat. However, with effort, a regular stethoscope can hear a fetal heartbeat.
A person deaf from birth would not know how loud a sound various actions would make, so likely could not deliberately live quietly. However, a deaf person with hearing aids or cochlear implants can make connections between collisions, vibrations etc. as making sounds. In addition to this, Regan would have been trained by her family to be very vigilant about potential noise-causing actions, as seen in her hearing brother's intense anxiety regarding making noise. It is also possible Regan was born hearing and became deaf later in life.
When Evelyn wakes up in the safe room with water flooding it and a creature in the opposite corner, not only is the lid inexplicably removed from the infant's safe box, but the oxygen mask is also no longer in use. If she was asleep & Lee left them there, the rising water would not have removed the lid and neither would the creature. Unless we are supposed to believe that since Lee felt it was safe enough to talk in this room and not be heard by the creatures that it was worth the risk of tempting fate by letting the baby openly cry, too, and not bother with the safe box they had assembled to guarantee it's safety after all?
The corn plants in the fields are green at day 472. This means they were planted in the current season. They have a full silo of corn, so there is no reason they would have needed to plant an entire field of corn to feed their small family. Also the perfectly aligned rows imply that they were planted by machine, which would have been extremely loud.
The opening scene takes place on "Day 89", while the remainder of the film occurs on or after "Day 472", or one year and 18 days later. But days 472 and beyond clearly occur earlier in the fall than day 89. As is noted in the "Trivia" section, the opening scene was filmed last because it required John Krasinski to shave off much of his beard, so it was indeed shot later in the fall. This anachronism could have been corrected by changing "Day 472" to, say, "Day 442".
In the fireworks scene, the (first) fireworks are supposed to be high in the sky above a cornfield, and the camera shot is from ground level (looking up). But you can see that the filmmakers simply superimposed fireworks over the cornfield, as the streamers are clearly in front of the corn plants.
The goof items below may give away important plot points.
Incorrectly regarded as goofs
Being totally blind, the creatures would be vulnerable to the shotgun the family owns , and the weapons every other American owns, it would be simple to stand silently in front of one, then when it is nice and close, just blow its brains out. However it is made quite clear in the film that the creatures have an impenetrable armored skin, like an outer shell. The only way Evelyn was able to kill one was when the high frequency sound waves caused the creature to open the armored shell up on its head exposing its soft inner tissue - and only then could she blow its brains out.
Seems very unlikely that no one in the government, especially any of the genius level scientists working for them, figured out that the best way to repel a creature with extremely sensitive hearing was to expose them to an extremely loud or high pitched sound.
When the monster went into the basement after Evelyn, not only would a being with super-sensitive hearing hear her panting, it would also hear the two heartbeats, one of the mother and one of the unborn child.