What is the best air purifier for a child with major allergies?

Air purifiers. The most effective air cleaners are the hepa filter type and the electrostatic air purifiers. The hepa filer traps most allergens in the filter so that clean air passes through. The electrostatics work by placing an electric charge on all particles coming into the filter and then passing them through metal plates that have an opposite charge so the particles are pulled out onto the plates.
Be careful. Electrostatic air filters release ozone, which is a known airway irritant, particularly in individuals with lower respiratory conditions such as asthma. Hepa air filters are preferable butt there are particular situations in which electrostaic (pet dander) filters may be more useful.