It sounds like mealtime is a lot of work for you, Irina. As long as you entertain your son, he will not go about the task of eating. It is very possible that he is not actually hungry when you set him at the table, but over the two hours, he starts to develop an appetite.
Keep his food portions very small so he isn't overwhelmed, but allow him to feed himself (he should be on table foods) and direct your attention to the rest of your family. He may be very demanding for a few meals, but be strong! When he realizes what he is there to do, he should settle down.
As for his weight, 9.5 kilograms (almost 21 pounds) is average for a 12-month-old boy, so please don't feel like he's not getting enough to eat.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.