Perhaps the kidnapper isn't really after harming the son but rather wants to use him to get something from the vampire world. Like, they need the son's unique vampire - human hybrid abilities to open a hidden vampire treasure or something. So, the son is in a strange position of being both in danger and also having some value that might keep him alive for a while.
One possible plot twist could be that the kidnapper is actually someone from their past who has a vendetta against them. Maybe it's a vampire who was wronged by the Cullens long ago and is now using their son as a pawn for revenge. This would lead to a tense situation where Edward and Bella have to face their family's history while trying to rescue their son.
Maybe the pregnancy is actually a part of a bigger plan by an enemy of the mob boss. They use Edward and Bella's situation to get to the mob boss, for example, by trying to kidnap Bella when she's most vulnerable. The mob boss then has to decide how much he's willing to risk to protect them.
It could be a rival vampire clan. They might see the son as a threat because of his unique nature, being part human and part vampire. They may think that as he grows up, he could become very powerful and pose a danger to their own power and territory in the vampire world.
One possible plot twist could be that Sasuke was actually being controlled by an unknown enemy when he kidnapped Hinata. This enemy might be using Sasuke's power to get to Naruto through Hinata. Another twist could be that Hinata has some hidden power or knowledge that Sasuke's side needs, and the kidnapping is a way to extract that from her. Maybe it turns out that Hinata was expecting the kidnapping all along as part of a larger plan to infiltrate Sasuke's group and learn their true intentions.
A plot twist could be that the place where the character is kidnapped has some hidden objects or clues that can only be found without glasses. For example, there might be a hidden message written in a way that is visible only to blurry vision. Also, the character might be kidnapped by someone they thought was a friend, and without their glasses, they initially mistake the kidnapper for someone else, which adds to the mystery and confusion. When they finally realize who it is, it's a big shock.
One possible plot twist could be that Mikey was kidnapped by an unexpected enemy, like a former ally who turned bad. Maybe it was someone he trusted, and this betrayal adds a layer of drama.
One possible plot twist could be that Jasper is being controlled by an external force, like a powerful vampire with mind - control abilities. So, he doesn't really mean to kidnap Bella in his true self.
One possible plot twist could be that Edward realizes that Bella represents a more 'normal' life for him compared to Fem Harry. Maybe Fem Harry has some dangerous or complex magical powers that Edward fears, while Bella seems more human and easy to understand.
One possible plot twist could be that the pregnancy is not natural. Maybe it was the result of some magical or supernatural interference. For example, a powerful witch cast a spell on them for some unknown reason.
One possible plot twist could be that Itachi has been mind - controlled to kidnap Sakura. Maybe an enemy of Konoha has a powerful jutsu that forces Itachi to do this against his will. Another twist could be that Itachi kidnaps Sakura as a means to protect her from a greater threat in the shinobi world that no one else is aware of yet. He might know that she has some sort of power or knowledge that makes her a target, and by kidnapping her, he can keep her safe in a hidden location.
One possible plot twist could be that the kidnapper is actually related to Naruto in some way. Maybe a long - lost relative who has some sort of vendetta against the Hidden Leaf Village and thinks taking Naruto will give them leverage. Another could be that the kidnapper is being controlled by a greater evil force that wants to use Naruto's special powers for their own dark purposes. For example, they might want to extract the Nine - Tailed Fox's chakra from Naruto while he's still a baby and vulnerable.