my son do not eat well , he just eat a plane chapatti with salt .... he eat no fruits and veggies......... how I develop his immunity??

Why with salt? Don't give salt like this... it's not good..... If he is hungry give him food which u prepares for urself... Like veg curry,, daal,, khichdi,, pulao,, chila, etc. If he refuses then leave him like that only... I know it's difficult for u... But he will eat what u will give him...if he's hungry.... So always give roti with curry or daal... N aalu parathas..., Try to make new dishes for him... Slowly he will eat food....

Yes first cut down the salt...
It's not healthy...

You can give vegetables by adding in rice,soups...
You can do parathas as well...
Make different dishes which are tasty and healthy...
And fruits you can give in to juices, milkshakes, fruit shakes,or directly...
You need to change his food habits...
And looks like your baby is 3.8 yrs old,now you can tell to him and explain...

You can also Google as mylittlemoppet or gkfooddiary it has many healthy recipes for babies and toddlers...

Egg or bes an +salt n tomatoo onion chilla banao or doh USko.boil Patatoo n veggies with black salt n lemon juice n kacha paaner,chicken n fish n sometime dry fruits.

Power vita by patanjali is good for health n digest

Asha Goswami ..... I tried my dishes with him everytime he vomits even if he was hungry for 5 hours ........ Totally tired with this

Then once check with the Paediatrician, sometimes due to worms in stomach also may not show interest in having foods...
So Dr can help you in this...