Recent studies suggest that five-year-old children can add and compare large numerical quantities through approximate representations of number. However, the nature of this understanding and its susceptibility to influence from canonical, learned mathematics remain unclear. The present study examined whether childrens early competence depends on the canonical problem format (i.e., arithmetic operations presented on the left-hand side of space). Children (M age = 5 years, 3 months) viewed events that required them to add and compare large numbers. Events were shown in a canonical or non-canonical format. Children performed successfully on all tasks, regardless of format; however, they performed better when problems were presented in the canonical format. Thus, childrens approximate number representations support arithmetic reasoning prior to formal schooling, but this reasoning may be shaped by learned mathematics.