How safe is the air coming? From humidifiers?

Safe if filter clean. Humidifiers are very helpful in kids with breathing problems.We need to ensure that their filters are clean.
Depends. If the water is clean and the humidifier is not contaminated by mold or bacteria the humidity it generates will be safe. When you invest in such a product, please read the accompanying instructions on cleaning and follow them.Mold loves water and over time any water source can become moldy.