What safety measure should Ms. Sun focus on to prevent poisoning in her classroom?

Focusing on confirming that toys are lead-free is a critical safety measure to prevent poisoning in Ms. Sun's classroom. Lead is a toxic substance that can cause serious health issues, particularly in young children who are still developing. By ensuring that all toys are free of lead, Ms. Sun can significantly reduce the risk of lead poisoning. This measure directly addresses the potential harm that can arise from toys made with hazardous materials, promoting a healthier and safer environment for children.

In contrast, the other options, while important for different safety or developmental reasons, do not specifically target the risk of poisoning. Durable toys may withstand rough play but do not address material safety. Bright and colorful toys can engage children but do not ensure they are safe from toxic substances. Lastly, regular maintenance for wear and tear focuses on the structural integrity of toys rather than the materials they are made of, which is essential but does not mitigate the risk of poisoning.