Factual error: Right after George Wilson kills himself with the revolver, the gun is seen falling into the fish pond in Gatsby's living room. Since Wilson shot himself in the head by placing the gun to the roof of his mouth, there is no possible way the gun could have flown so far away from his body, especially without getting bloody.
Factual error: In the opening sequence, as Nick arrives at Tom and Daisy's shore to meet Tom, there are people playing/practicing polo in the background. The ground is undulating where polo must be played on a flat field, both for the ball to roll consistently and for the safety of the riders and ponies.
Answer: I would say Gatsby knew about the child but suddenly realised she had a life without him and that she loved her children so her leaving was not going to be as easy as he imagined. Gatsby sees both Daisy and Tom in this scene being loving parents (for a minute or so) and it was hard to witness.