It is advisable to consult a dietician on what is perfect for an underweight child. Before listening to other mothers, it is important to consult a doctor because what worked for their children may not necessarily work for your toddler. Specialized doctors give accurate advice on how to improve the state of your underweight child and hardly do their recommendations ever fail, if followed with the utmost dedication.
Lastly, having underweight children is not unusual. Therefore, you do not need to be worried or get stressed about it because it can be dealt with by necessary action after good and suitable consultation process.