The present study aims to examine relations between number representations and various sources of individual differences within early stages of development of number representations. The mental number line has been found to develop from a logarithmic to a more linear representation. Sources under investigation are counting skills and executive functions and are set out against mental number lines from 0 to 10 and 0 to 100 in a sample of 4- to 8-year-old children (N = 80). Findings indicate that counting skills, inhibition, and updating are the most important predictors of the shape of the mental number line over and above age-related developmental differences, with number lines from 0 to 10 being linear to a large extent and number lines from 0 to 100 developing from a random pattern toward logarithmic representations. The shape of the mental number line was found to predict scores on the number comparison task only on the smaller-scale comparison task.