Part of a demonstration organized by People for the Ethical Treatment of Animals, the costumed protester waved and handed out coloring books at Colfax Elementary School in Squirrel Hill, Pa., the Pittsburgh Tribune-Review reported.
The aim of the appearance was to persuade children and their parents to boycott an appearance by the Ringling Bros. & Barnum Bailey Circus in Pittsburgh next month, the newspaper said.
Some parents said they were not comfortable with the action.
"I generally support PETA, but I don't believe demonstrating outside an elementary school is the proper venue," said Sabrina Weihrauch, 48, the parent of a Colfax student. "This is not the way to go about it."
"They're hustling little kids," said Anne Myrick, 72, of Penn Hills, who along with Colfax Principal David May-Stein tried to direct students away from the demonstration.
"I'm not going to let them suck these kids in," Myrick said.
PETA spokeswoman Virginia Fort said the message was intended to "gently let children know" how circus elephants are treated.
A child psychologist said the protest could have confused or even traumatized the youngsters.
"It sounds pretty inappropriate to me, especially since you can't predict how a child is going to perceive the image," Scott Leatherby, who specializes in children's issues, said.