To investigate the development of the NP selection process, preferences for overt or null Spanish subject pronouns were elicited from 139 children (5;09 to 15;08) and 30 adults in Mexico. Participants were told stories in which consecutive grammatical subjects shared the same referent (same-reference), or did not (switch-reference). In the stories, overt pronouns in same-reference were redundant, and null pronouns in switch-reference rendered reference ambiguous. Adult participants preferred null pronouns in same-reference contexts and overt pronouns in switch-reference contexts, demonstrating an avoidance of redundancy and ambiguity. Children demonstrated a tolerance for redundancy well into adolescence. A tolerance for ambiguous reference declined at age eight/nine and then progressively decreased with age. We interpret the tolerance for ambiguity as an indication that children have difficulty with perspective taking when faced with complex structures and tasks. (Contains 1 figure, 8 tables, and 20 footnotes.)