Continuity mistake: Spoiler Alert: When Finney digs the hole through the wall with the toilet tank cover, he creates a relatively round hole to the back of the refrigerator. After climbing into the hole and then back out, the hole is now almost perfectly square. (01:16:38 - 01:17:28)
Suggested correction: I agree that the appearance of the hole changes, but I wouldn't say it went from "relatively round" to "almost perfectly square." (The appearance is probably due to the camera's angle). The hole started out as oval-like but progressed to a rectangular shape with curved corners. When Finney came back, the rectangular shape had squarer corners and straighter/neater edges. [The wording should be changed for accuracy, but I won't edit your wording.].
Character mistake: In the very beginning at the baseball game the runner is running to second base and the fielder doesn't even try to tag him out. Just runs right by him and gets the ball to the pitcher. (00:00:53)
Suggested correction: The center fielder missed the ball and the right fielder got it. The second baseman was at the border of the infield and outfield and the right fielder may not have noticed that the short stop moved to cover second base. By this time, the players might have been more concerned over the opposing team scoring a run because a player had advanced to third base. It was a "revealing" mistake or overall "stupidity" by the team as each player was playing "musical positions" more so than good baseball.
With regard to "revealing", the players may have been instructed to be active on the field and cover bases for each other as needed and this was the "mess" they produced.
Suggested correction: Baseball players make mental errors all the time, even major leaguers.
I've watched the scene a few times and can't agree or disagree with the mistake, but it certainly doesn't look like a mental error one would see in a game, even a little league game. It just looked like two kids were given directions what to do and the timing might have been off and the director on set didn't bother changing it. (I'm not disagreeing or agreeing with the correction either, just making a statement to help others decide).
Factual error: On Saturday morning Gwen and Finney were watching cartoons. This was the day after she spent the night at her friends house which was a Friday night. The cartoon that was on the TV was Davey and Goliath. This cartoon only aired on Sunday mornings.
Suggested correction: "Davy and Goliath" aired on Saturday or Sunday mornings, depending on the TV station. And, according to Wikipedia, it "premiered in syndication on 2/25/61 as a Saturday feature."