Although variability is a core concept in statistics, little is known about young children’s understanding of statistical variability. This study investigated the effect of variability on children’s performance in a quantity judgment task. Participants were 110 children (49% boys) aged 4-6 years living in Northern Italy. Children were individually assessed using a computerized task in which they were asked to compare the quantity in two sets of chocolate bars. The lengths of the chocolate bars varied (which makes the task hard) and the variance of the lengths was manipulated. Children also completed a standardized test of numerical ability. Main results indicate that children’s performance on the judgment task: 1) is affected by variability non-monotonically; and 2) is only moderately correlated with numerical skills.