Thanks for asking . I gone through question. your 2.5 year old son not feed properly If i was your treating pediatricain . then i would like to ask about his daily intake, from wake to sleep in actual quantity. and his weight and height. plot in growth chart. ( you also can do it, charts are availble on CDC site) it the weight and height are in normal range,then no thing active intervention required, There no such medicine is advised that improve appetite. The rate of weight gain in reduced after one year of age. in first year of life weight gain is approx 7 kg (birth weight approx 3kg and weight of one year of infant is 10kg) , and in second year weight gain is just 2 kg. Children have small capacity in stomach so they each less in one time. we should offer them frequently.and children are very choosy . trying more and more things increases chance of to accept the feeding