To familiarize children with the apparatus, sounds and requirements of fMRI testing, children performed a training session prior to the actual fMRI experiment in a mock‐scanner at the Max Planck Institute for Human Development (see Raschle et al., 2012, for an outline). During the training, we explained the functioning of the scanner, the experimental pipeline, and the negative effects of extensive head movement on scanning results. Approximately a week later, children returned for a second session at the Center for Cognitive Neuroscience Berlin (CCNB), in which the actual fMRI experiment was conducted. The experiment was divided into four runs, with the four visual and the auditory conditions presented block‐wise (15 stimuli per block). To ensure children's attention, a catch trial was performed at the beginning of each block (150 ms), in which a picture of the mascots of the project was shown and children were instructed to press a button using their middle or index finger to confirm its appearance. Average performance on the catch trials for the cohort of 54 kindergarten children was .67 (range = 0–1, SD = .31). As indicated by the range of performance, the mean value was strongly influenced by a few children that did not manage to respond; they may possibly have been mentally overstrained by the highly new and demanding situation, or simply forgot to press the button. In any case, when asked afterwards whether they noticed the mascot, all of these children confirmed that they had. As such, the data from those children was kept for further analyses. Catch trials were followed by a jittered fixation cross (300–600 ms) and then replaced by the first stimulus. Visual stimuli were shown for 500 ms and auditory stimuli were presented for 500–600 ms. Each stimulus was followed by an inter‐stimulus interval of 200 ms (fixation cross). Three to five null‐events were included in each run to allow the blood‐oxygenation‐level dependent (BOLD) signal to return to baseline (2–14 s, 26 s per run). Each run took about 136 s and was followed by a short break to improve compliance and maintain attention of the children (see Figure S1 for a schematic overview of the fMRI design). The order of the stimuli and null‐events was optimized using the optseq2 algorithm (Dale, 1999). The order of blocks was pseudorandomized within runs, and the order of runs was counterbalanced across subjects. The session was completed by a high‐resolution structural scan during which children could relax and watch a short movie. The entire scanning session lasted for about 15 min.

Imaging was performed using a 3.0 T Siemens Magnetom Tim Trio scanner (Siemens, Erlangen, Germany) equipped with a 12‐channel head coil. In each of the four runs, 68 whole brain functional T2*weighted echoplanar (EPI) pulse sequences (TE: 30 ms, TR: 2000 ms, 70° Flip Angle, 37 slices, matrix: 64 × 64, field of view: 192 mm; 3 × 3 × 3 mm3 voxel size, 20% interslice gap) were acquired, resulting in a total of 272 axial volumes. Additionally, a T1‐weighted matched‐bandwidth high‐resolution anatomical scan with the same slice prescription as EPI was acquired (176 sagittal sections, 2 × 2 × 2 mm3 voxel size, matrix: 256 × 256). The standardized pictures were presented at the center of a white screen on dual display goggles (VisuaStim, MR Research) using Python 2.7 (Python Software Foundation). Auditory stimuli were presented via circumaural earphones (VisuaStim, MR Research). To attenuate scanner noise, child‐appropriate earplugs were provided, and the children's heads were padded with foam to improve their comfort and reduce motion artifacts.

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