This study investigated the ASPECT FIRST HYPOTHESIS which claims that children initially use verbal morphology to mark aspect and not tense. Experiment 1 tested 46 two- and three-year-old children's comprehension of tense as it is marked in the auxiliary system using a sentence-to-scene matching task. Children were presented with multiple performances of the same event and asked where a character is V'ing, was V'ing and is gonna V. Results showed that even the two-year-old children could successfully understand tense in this experiment. Experiment 2 changed the information available in the scenes by varying whether or not the past-time event reached its completion point. Thirty-six two-, three- and four-year-old children participated. The results showed that the two-year-olds could only successfully understand past and present auxiliaries when past-time information in the scenes was co-extensive with completion information in the scenes. This result suggests that these children may be making a grammatical aspect (perfective/imperfective) judgment and not a tense (past/present) judgment, or at least, that grammatical aspect influences tense interpretation for these children.