Honestly it depends on the game and the people who are working at the game, they are usually super nice and if the child is small enough (and they don't think you are tricking them to take the kid in the game) they may let you in.
If the child doesn't meet the height requirements they might not let him pass into the line, regardless if they're not even getting on the ride. If they do let the child pass then someone will have to wait in the line with the child while the other adults ride, that way they can pass the child over to the first group who rode so they can exit with the child while the adults who waited can go on the ride.
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