This article compares many of the differences, in continuity, and by fan retcons/story changes/artistic license made by the game (compared to the canon original games and material), as well as comparing screens from different games, and showing differences between the fan game and the original Sierra material.
See also IF universe, Js universe, AGDI universe, POS universe, and IA universe for similar comparisons between other fan games and the original series. And KQ1 comparisons, KQ5 comparisons, TOG universe (Dragon's Lair comparisons) for similar comparisons between official remakes, ports and adaptations.
This game's storyline takes several liberties from the official continuity. One liberty is how the baby was kidnapped, in official continuity Manannan kidnapped the baby himself teleporting into Daventry and casting a sleep spell on the family while he stole the baby. In this game it was two strange men who grabbed him and took him across the mountains, and crossed the seas to Llewdor.
Another liberty is when the kidnapping took place, in this story it happens eight days after he was born, in official continuity it was at least six months after he was born.
According to King's Quest 3, the magic mirror went black after Alexander was kidnapped, and never worked again until his return. In this game it works, even if briefly, to show Valanice her son and the fact that he was ill. Later after she "saves" Alexander by breast feeding him, the mirror shows her that he survived.
The biggest issue has to do with the fact that Valanice never knew where Alexander was taken in continuity. They had searched around Daventry for months, before giving up. In this game she tracks down his kidnappers, all the way to Llewdor. She is able to breast feed Alexander, and sings a song the boy, explaining to him how he can make it back to Daventry when he is older. She attempts to take the baby, but is killed by the men, and ends up in the Land of the Dead (unofficial) (however she is able to regain her life, and escape back into Daventry).
At one point Valanice is killed, but is able to dig herself out of the Realm of the Dead (unofficial) exiting with a new physical body. This seems rather easy way out of the afterlife compared to what it takes for Alexander to escape and winback the souls of Caliphim and Allaria.
The story has a rather large plot hole, which begs the question if she knew who was behind the kidnapping, and where her son was taken to, then why didn't she just pull together Daventry's army and head back to save her child... Of course in the official continuity she never knew he was in Llewdor.