In this paper, we tested the resource dilution hypothesis, which posits that, because parenting resources are finite, the addition of a new sibling depletes parenting resources for other children in the household. We estimated growth curve models on the self-reported parenting practices of mothers using four waves of data collected biennially between 1994 and 2000 on a nationally representative sample of 2,082 Canadian children aged 2 to 5 at initial interview and in continuously intact, two-biological-parent households. Results showed that when new children were added to the household, mothers exhibited declines in positive interaction, but increased their levels of consistent parenting. Taken together, these findings suggested that parenting resources were reallocated, rather than diluted, when family size increased.