A 6-year-old child complains of pain in the right submandibular region. A day before he complained of a sore throat. Objectively: the child is in moderately severe condition, body it is 37,9°C. The face is asymmetric due to a dense tender infiltrate in the right submandibular region. The infiltrate is slightly mobile, the overlying skin is hyperemic. There is fluctuation in the center. The teeth are intact. What is the most likely diagnosis?