**Calgary Preschool MRI Dataset** The Preschool MRI study in The Developmental Neuroimaging Lab at the University of Calgary (https://www.developmentalneuroimaginglab.ca) uses different magnetic resonance imaging (MRI) techniques to study brain structure and function in early childhood. The study aims to characterize brain development in early childhood, and to offer baseline data that can be used to understand cognitive and behavioural development, as well as to identify deviations from normal development in children with various diseases, disorders, or brain injuries. The MRI techniques used include diffusion tensor imaging (DTI), anatomical imaging, arterial spin labeling (ASL), and resting state functional MRI (rsfMRI). All imaging for this dataset was conducted using the same General Electric 3T MR750w system and 32-channel head coil (GE, Waukesha, WI) at the Alberta Children’s Hospital in Calgary, Canada. Children were scanned either while awake and watching a movie, or while sleeping without sedation. The University of Calgary Conjoint Health Research Ethics Board (CHREB) approved this study (REB13-0020). **DTI b750 Dataset** The DTI dataset here comprises 396 unprocessed b750 diffusion weighted MRI scans from 120 participants aged 2-8 years. An accompanying excel sheet in the dataset information folder provides age (years) and biological sex (female = 0; male = 1) information for each participant and scan. A B-matrix and .bval/.bvec files for the dataset are also located in this folder. Whole-brain diffusion weighted images were acquired using single shot spin echo echo-planar imaging sequence with: 1.6 x 1.6 x 2.2 mm resolution (resampled on scanner to 0.78 x 0.78 x 2.2 mm), full brain coverage; TR = 6750 ms, TE = 79 ms (set to minimum for the first year of data collection), 30 gradient encoding directions at b=750s/mm2, and five interleaved images without gradient encoding at b=0s/mm2, for a total acquisition time of approximately 4 minutes. **ASL Dataset** The ASL dataset here comprises 279 unprocessed ASL perfusion scans from 96 participants aged 2-7 years. An accompanying excel sheet in the dataset information folder provides age (years) and biological sex (female = 0; male = 1) information for each participant and scan. During the scan, children watched a movie of their choice. T1-weighted images were acquired using an FSPGR BRAVO sequence with TR = 8.23 ms, TE = 3.76 ms, TI = 540 ms, flip angle=12 degrees, voxel size = 0.9x0.9x0.9 mm3, 210 slices, matrix size=512x512, field of view=23.0 cm. ASL images were acquired with the vendor supplied pseudo continuous 3D ASL sequence with TR = 4.56 s, TE = 10.7 ms, in-plane resolution of 3.5x3.5 mm2, post label delay of 1.5 s, and thirty 4.0 mm thick slices. The sequence scan time was 4.4 minutes. **Passive Viewing fMRI Dataset** Passive viewing fMRI data were collected with a gradient-echo echo-planar imaging (EPI) sequence, 3.59 × 3.59 × 3.6 mm resolution, 36 axial slices, TR = 2000 ms, TE = 30 ms, flip angle = 60°, matrix size = 64 × 64, slice timing order: interleaved (i.e., 1 3 5 7 9 2 4 6 8 10), 250 volume, for a total acquisition time of 8:20 min:sec. The first 10 volumes were removed in the shared NIFTI file due to the environmental adaptation. Children were watching a movie of their choice during the scan (movie choice was not recorded). **Funding** CIHR (IHD-134090) CIHR (MOP-136797) University of Calgary **Related references** https://doi.org/10.1101/524785 https://doi.org/10.6084/m9.figshare.7603271.v1 http://doi.org/10.3389/fped.2018.00146 https://doi.org/10.1016/j.bandl.2017.10.008 https://doi.org/10.1016/j.biopsych.2015.12.004 https://doi.org/10.1101/587139 Correspondence: clebel@ucalgary.ca