Goofs

During the graveyard scene between David and Alan, it is clear (because of changes in the amount of light, and the angle of sun in the background, as well as cloud cover) that this particular scene was shot over a period of several hours or possibly days.

Mara's white tights become blue anklets during her first visit to the Midwich Clinic.

As the people lay unconscious near the beginning of the film, we see Melanie Roberts lying next to the bathtub. The bathtub is filling with water, which would seem to indicate that she has yet to take a bath. Yet she is shown lying next to the tub, wearing a towel with wet hair.

Melanie Roberts is dry (but still wearing the towel) while laying next to the filling tub when the blackout started. When she woke up, she had wet hair because her tub had overflowed and she was laying in a puddle of water.

the entire time the movie was playing there were only 7 children and with 15 minutes left when the townspeople were marching with the torches, like they were going after Frankenstein, there are 6 children outside in a line confronting the townspeople with their evil eyes and there are 3 children inside with Dr. Verner checking out the alien and that's a total of 9 children, what is going on here?

Baby Mara, has dark brown eyes, older Mara has light blue eyes.

During the Janitor death scene, it is clearly a dummy which lands on the car.

When the eye doctor mistakenly uses the wrong substance instead of eye drops, the girl's eyes remain shut but she still screams in pain as if something is burning her eyes.

At around 91 minutes. As Jill and David crouch by the car during the explosion, the clapboard can be seen reflected on the side of the car.