Mine isn’t staying closed. Is there a trick or is mine defective?

If everything is closed up inside then it should close all the way and stay. Also, check that your people and swans aren't getting into the hinge when you close it. That could make it pop open. Otherwise, yours may be defective.

Do polly pocket toys conform to safety certifications like astm or ce?

You can find a more detailed response at the Mattel Corporate site, but the short answer is yes. Polly Pocket toys follow all safety guidelines. In addition, Mattel has a 450 member team that overseas safety and compliance. “ Mattel’s Quality Team is comprised of approximately 450 professionals and overseen by our Head of Product Quality, Safety, and Compliance. It includes engineers, product safety specialists, compliance experts, test laboratory personnel, child development experts, and others involved in product development and manufacturing. They are responsible for the overall Mattel quality system, safety compliant management, product risk management, governmental safety reporting, recall management, auditing of quality systems, regulatory assurance, and ethical and social compliance. The Quality Team documents the requirements and specifications that each product must meet, including regulatory and voluntary standards, as well as internally developed safety and testing standards that are based on years of experience producing children’s products.”