Heavy metals like lead, mercury, arsenic, and cadmium are environmental toxins that can accumulate in the body over time. Children are particularly vulnerable because their bodies are still developing, and their nervous systems are more susceptible to damage from these toxins. Signs and symptoms of heavy metal toxicity in children include hyperactivity, impulsivity, aggression, anxiety, depression, developmental delays, speech delays, fussy or restrictive eating, poor sleep, digestives issues and weakened immune system.