The null subject (NS) stage is one of the best-described hallmarks of first language development. We present a series of experiments assessing children’s interpretation of NS sentences, as a way of testing the two main competing analyses of the phenomenon: grammatical accounts, under which young children’s grammars license NSs in declarative sentences; and performance accounts, which hold that children have an adult grammar, but omit subjects in production for extrasyntactic reasons. Overall, we find evidence of an NS stage in comprehension, just as in production. This suggests that child and adult grammars differ, in line with grammatical accounts.