In part 43 of the analysis, the possibility was raised that Molly is not Kevin's natural mother, the reasoning being that if her hair is naturally curly, then she cannot have a straight-haired child (Kevin has straight hair). However, note that she and Kevin have a fairly strong facial resemblance (see above screencaps). What must be the case is that Molly's hair is not naturally curly, and that she is Kevin's natural mother. The reason she's been keeping her hair curly is because she doesn't want Will to know that she is Kevin's natural mom. It is when she is around Will that her hair is more curly; during time periods that Will is away, she 'let's her hair go', i.e., she does not keep curling it. The reason there's a pin holding her hair in back when she and Kevin have first been relocated, is because she has been rushed to the new location from the Graham home in Captiva, and thus, she did not have time to re-curl all of her hair. Recall that we already determined she was hoping to see Bloom when she answered her door in Captiva; he knows that she doesn't have naturally curly hair.
Above left and right: These two screencaps from the scene in Captiva at the beginning of the movie, show that when Will is around, Molly keeps her hair quite curly (click to enlarge).
Above left and right: Later in the movie, Molly has been expecting Sidney Bloom to arrive in Captiva, and since Will has been away, she hasn't been keeping her hair curled.
Above left and right: Not much later than the above, upon being relocated from Captiva, Molly is still trying to lead Will to believe that her hair is naturally curly. However, she has only had short notice prior to the relocation, so she has only had time to re-curl the front part of her hair, which is why she has it pinned in back and tied in a makeshift ponytail.
Above left and right: Later, while conversing with Will on a dock at the new location, Molly has now let her hair go in the presence of Will. She is no longer trying to fool him - she has admitted to him that she is Kevin's natural mother. The reason this is an important admission is bound up with another fact that Molly admitted to Will at the new residence - a fact which Will already knew prior to her admission; this fact and how Will came to know it, is soon to be discussed.
