There is a theory that if your body is not exposed to enough good bacteria and other pathogens then it will build up an army to fight out non important things like pollen and peanuts. I would recommend giving kids probiotics and also not keeping environment so clean with wipes and excessive hand washing that they never get exposed to good and some bad germs.
This correlation is often referred to as the 'hygiene hypothesis' by researchers. The underlying cause is still being understood; you can find an article comparing two theories here [0].
