The correct answer is option 'C': they show vastness which is opposite to the world and needs of the children in the classroom.

Explanation:
In the context of the question, the pictures and maps are considered meaningless because they depict vastness, which is contrary to the world and needs of the children in the classroom. Let's break down this explanation further:

1. The Opposite of the World and Needs of Children:
The world inside a classroom is typically confined and structured, with limited space and resources. Children in a classroom require a focused and interactive learning environment that caters to their specific needs, rather than overwhelming them with the vastness depicted in pictures and maps.

2. Vastness Depicted in Pictures and Maps:
Pictures and maps often portray expansive landscapes, seascapes, or geographical features that may not relate directly to the immediate surroundings of the children in the classroom. These visuals can be distracting and may not align with the curriculum or learning objectives. The vastness represented in these mediums can also create a sense of disconnection or detachment for the students.

3. Lack of Relevance and Engagement:
The pictures and maps may not hold immediate significance or relevance to the topics being taught in the classroom. They might not stimulate the students' interest or engage them in active learning. To promote effective learning, it is important to provide visual aids, such as images and maps, that are relatable and meaningful to the students' learning experiences.

4. Need for a Stimulating and Contextual Learning Environment:
To foster meaningful learning experiences, it is crucial to create a classroom environment that is stimulating, contextual, and relevant to the students' lives. This can be achieved by incorporating visuals that align with the curriculum, capture the students' attention, and facilitate their understanding of the subject matter.

By considering the world and needs of the children in the classroom, the pictures and maps can be deemed meaningless if they fail to fulfill the criteria of relevance, engagement, and alignment with the curriculum. Therefore, option 'C' is the correct answer.