probiotic for children is good for the immune system
If you have not already, cut out all refined sugars from his diet. Sugar wreaks havoc on the immune system. Other than that, you could try omega 3 fatty acids and echinacea.
I would recommend a homeopathic physician. The remedies are diluted down to nothing so it won't hurt him, and this could partly be a response to antibiotics if they've been used more than once. I wouldn't use echinacea too much for a child or adult; regular use can overtax the immune system. It's only meant for occasional use. But for small children, I'd still go with homeopathy first. Also, did you breastfeed? If not, the child didn't get his early immune system, and you might want to look into a supplement called colostrum.
Colostrum is the fluid that new mothers' breasts produce during the first day or two after birth. It gives newborn infants a rich mixture of antibodies and growth factors that help them get a good start.
Although colostrum has been available since the first mammals walked the earth, it is relatively new as a nutritional supplement. The resurgence of breastfeeding in the 1970s sparked a revival of interest in colostrum for both infants and adults.
However, most commercial colostrum preparations come from cows, not humans. The antibodies a mother cow gives to her calf are designed to fend off bacteria that are dangerous to cows; these may be very different from those that pose risks to humans. Nonetheless, colostrum also contains substances that might offer general benefits, such as growth factors (which stimulate the growth and development of cells in the digestive tract and perhaps elsewhere) and transfer factor (which may have general immune-activating properties). In addition, some researchers have used a special form of colostrum called hyperimmune colostrum, created by inoculating cows with bacteria and viruses that affect humans. The cow in turn makes antibodies to them and secretes those antibodies into its colostrum. Hyperimmune colostrum has shown considerable promise as an infection-fighting agent.
Hyperimmune colostrum, however, is not available over-the-counter as a dietary supplement. Non-hyperimmune colostrum might have some value too, but the evidence is much weaker.
I'm not sure, but I think there's a goat milk colostrum. At least I remember one. Still not as good as human milk, but better than cow. Am I mis-remembering this?
There are many herbs and product that will promote a good immune system. Some of them include Sambucus Black Elder Berry extract, Beta D-Glucan, Mushrooms complex, Ascorbil Palmitate, Echinacea etc.
But since it's for a children i would go with Vitamin C, which can be obtain with vitamin supplement ( try looking up Nature's Plus, Source of Life, Animal Parade, Children's Chewable Vitamin C, Natural Orange Juice Flavor ) or by including a lot of fruits in his diet. Vitamin C is extremely good at boosting the immune system. I would also have a look at Herb Pharm's Children's Echinacea, Alcohol-Free, Orange Flavored liquid formula, Planetary Herbals, Well Child, Immune Chewable, 570 mg ( half doses ).
I wouldn't consider homeopathic medicine because of the simple reason that it's only water with no specific medicine and it's not proven scientifically and will never be. Homeopathic power remains in the placebo effects and such effects won't happen in your 2 years old kid. For homeopathy to be more than water it would have to violate the laws of chemistry and physics such as the law of mass action and the chemistry laws that there is a limit to the dilution that can be made without losing the original substance ( all that is left into homeopathic remedies is water and only water ) .
Physicist Robert L. Park, former executive director of the American Physical Society, has noted that
“since the least amount of a substance in a solution is one molecule, a 30C solution would have to have at least one molecule of the original substance dissolved in a minimum of 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 molecules of water. This would require a container more than 30,000,000,000 times the size of the Earth.''
Park has also noted that "to expect to get even one molecule of the 'medicinal' substance allegedly present in 30X pills, it would be necessary to take some two billion of them, which would total about a thousand tons of lactose plus whatever impurities the lactose contained"