My daughter is 2.5 years old. She can sit still for the 1st half bowl of rice, and then she requests me to feed her for the rest of the bowl.
Recalled that I tried to train her up while she was smaller. I rewarded her "sweet" or "ice-cream" after she sit still for the meal. Then, for the time being, she knows she has to sit and eat and then play unless those food she doesn't like, she will lose patience to sit still.