Children have symbolic arithmetic before formal instruction

The editor's summary of an interesting paper in Nature by Gilmore et al.:

It is commonly assumed that young children need to master the logic of number systems before learning symbolic arithmetic. Now a trial using 5-year-old children suggests that in fact they have symbolic arithmetic knowledge before they have received any arithmetic instruction. The children are capable of solving symbolic addition and subtraction problems with large numbers, provided that only approximate sums and differences must be computed. These findings shed light on the numerical competences that come naturally to children, and suggest ways to enrich children's learning of mathematics.