Background: Full model-based iterative reconstruction (MBIR) algorithm decreasing image noise and improving spatial resolution significantly, combined with low voltage scan may improve image and vessels quality. Purpose: To evaluate the image quality improvement of pulmonary vessels using a full MBIR in low-dose chest computed tomography (CT) for children. Material and Methods: This study was institutional review board approved. Forty-one children (age range, 28 days-6 years, mean age, 2.0 years) who underwent 80 kVp low-dose CT scans were included. Age-dependent noise index (NI) for a 5-mm slice thickness image was used for the acquisition: NI = 11 for 0-12 months old, NI = 13 for 1-2 years old, and NI = 15 for 3-6 years old. Images were retrospectively reconstructed into thin slice thickness of 0.625mm using the MBIR and a conventional filtered back projection (FBP) algorithm. Two radiologists independently evaluated images subjectively focusing on the ability to display small arteries and diagnosis confidence on a 5-point scale with 3 being clinically acceptable. CT value and image noise in the descending aorta, muscle and fat were measured and statistically compared between the two reconstruction groups. Results: The ability to display small vessels was significantly improved with the MBIR reconstruction. The subjective scores of displaying small vessels were 5.0 and 3.7 with MBIR and FBP, respectively, while the respective diagnosis confidence scores were 5.0 and 3.8. Quantitative image noise for the 0.625mm slice thickness images in the descending aorta was 15.8 +/- 3.8 HU in MBIR group, 57.3% lower than the 37.0 +/- 7.3 HU in FBP group. The signal-to-noise ratio and contrast-to-noise ratio for the descending aorta were 28.3 +/- 7.9 and 24.05 +/- 7.5 in MBIR group, and 12.1 +/- 3.7 and 10.6 +/- 3.5 in FBP group, respectively. These values were improved by 133.9% and 132.1%, respectively, with MBIR reconstruction compared to FBP reconstruction. Conclusion: Compared to the conventional FBP reconstruction, the image quality and diagnostic performance for pulmonary vessels was significantly improved by the MBIR reconstruction in low-dose chest CT in children.