Asthma and the Immune System

I have a 4 year old with asthma which only flares up with a cold. It usually turns into respiratory infection, bronchitis or pneumonia. What can I do to help my 4 year old? I have another child who is 5 years old and rarely gets sick. They are both in daycare. What can I do? I tried the echinacea. What else can I try?

Asthma is a hypersensitivity reaction, often to allergens such as animals, pollution, perfume, oranges or dust and aggravated by tension and cold. The airways become inflamed and constrict, making breathing difficult. Food allergens that may cause the hypersensitivity, and should be avoided, are dairy products, fatty meat, eggs, food additives and chocolate. Soy products can replace dairy products, and a few vegetarian meals a week will reduce fat intake.
Diet changes are the most effective way to improve health in asthma. The diet should be high in fresh fruits and vegetables. Sugar products should be avoided because sugar decreases immunity. Foods high in essential fatty acids, such as beans, lentils, sunflower seeds and nuts will promote the health of the body cells. Possible allergens, dairy products in particular, should be avoided until health is regained.
As well as Echinacea, which is excellent support for the immune system, you could use:
Thyme: antibacterial, antiviral, especially effective in infections of the respiratory system
Chamomile is calming, anti-inflammatory and helps the digestive system, which may be weak due to allergies.
Wild Indigo: very safe, strong decongestant and immune stimulant.