The mathematical construct of dimension is one of the fundamental ideas for developing a sound understanding of two-dimensional (2D) and three-dimensional (3D) shapes. Yet, research in mathematics education has rarely explored children's understanding of dimension in primary education. This paper explores how year 5/6 (9 to 11 years old) children construct and negotiate their meanings about dimension while engaging in classroom interactions about 2D and 3D shapes during geometry lessons in a New Zealand (NZ) English-medium multilingual primary classroom. Transcribed data of two key moments selected from six audiovisually recorded geometry lessons are presented. The findings suggest that children may use different discursive constructions--"another world", "different ways to go", and "flat vs fat"--to display their meanings about dimension. The findings also suggest that children and teacher participants may use prosodic features of their languages to interactionally construct the meanings of these discursive constructions. The paper discusses these findings in light of current research literature and offers a few implications for curriculum development and future research.