The main character is most likely the little lost angel. However, depending on the nature of the story, there could be other important characters. For example, if it's a story set in a human world, there could be a human child who befriends the lost angel. Or there could be a wise old owl in a forest where the angel is lost, which serves as a mentor figure. There could also be a villainous character, such as a demon who wants to corrupt the pure little lost angel.
Not having read the actual 'the little angel story', I can only guess. The little angel is surely a main character. There could be a devil - like character if it's a story about good versus evil. And there might be a group of friendly animals in the story that the little angel befriends and helps. The story could be centered around how the little angel affects the lives of these different characters.
As I don't know the specific story, it could have elements like a vulnerable character (the little lost angel), a setting where they are lost (maybe a forest or a big city). There might also be some characters who help or hinder their journey.
The most obvious main character is the little bear. Since it's a 'lost' story, the bear's family, especially its mother, could be considered main characters too as their absence (from the little bear's perspective) is a big part of the story. There could also be other animals in the forest that the little bear meets during its lost time, but they may be secondary characters.
Obviously, the little lost penguin is a main character. There might also be its parents or siblings who are worried about it and are looking for it.
The main character is obviously the little lost puppy. And usually, there is also the puppy's owner who is worried and searching for the puppy.
I'm not sure specifically, but it could be the little lost robot itself as the main character. Maybe there's also an inventor or an owner who is looking for the robot.
The little girl is the central character. Maybe there is a friendly stranger in the story. This person could play an important role in helping the little girl, or at least trying to help her find her way. There could also be some animals that she encounters during her lost time, which could be both helpful or a hindrance.
The main character is the little boy. But depending on the setting of the story, there could be other important characters. For instance, if it's set in a forest, there could be forest animals like a wise old owl or a friendly deer that the boy encounters. These animals could play a role in either helping the boy find his way or leading him further astray. Also, there could be other humans in the story, like a ranger or a hermit who lives in the forest and has some knowledge that can assist the boy in getting back to safety.
The main character is surely the little lost lamb. There might also be the shepherd who is looking for the lamb or the other lambs in the flock that the lost lamb is separated from.
In a story like this, there could be a mentor - like figure for the little lost lord. This character could be someone with knowledge of the area where the lord is lost or someone with special skills. Also, there might be other lords or nobles who are involved in the events that led to the little lord getting lost in the first place, so they could also be considered main characters in the broader context of the story.