My 7 year old son falls sick easily upon attending K1 onwards, what could be the reasons?

Could be because he is over stimulated from being active and having fun in school. Add that to the exposure of a new environment, your young son is bound to fall ill every now and then. But as he grows older, his immunity will be stronger so don't worry. You can boost his immunity by ensuring that your son gets alot of vitamin c through veggies and fruits or even vitamins. Make sure he drinks lots of water and if you like, you can introduce more essential fatty acids in his diet (salmon, cod oily fish) as these will contribute to the production of white blood cells that help fight germs and infections.