Hello. I Have A 19 Month Old Baby Boy. He

Hello. I have a 19 month old baby boy. He is completly on motherfeed. Aabout two months back, he was eating fine and gaining mass.but recently he has stopped eating. He will go on picking food all day lomg but wont have one good meal. He has lost all his mass and even shed 1 kilo... my mom suggested me to give mosegar to him. How much should i give him and how often? Other than being sleepy are there other reportrd side effects? Really worried