my son is 3 and half year ...and his weight is only 11.50 kg... please suggest how to increase weight..also he don't eat any fruits

A. Hello mom a little variation is always acceptable. As far as the child is active for their age and eating well kids this age tend to be pricky eaters. Try to present the usual foods in different ways and forms to them to make it more. Interesting. Also gradually increase the quality of the food given to them of a different variety and flavours of food.