How Long Will Child S Lymph Nodes Stay Swollen?

hi doctors, i have a son 5 to 6 years old. just before 4 months and after having a flue, we noticed a movable and small pea sized nodes in both side of his sub-mandibular. i took him directly to a doctor. After checking him by touching the nodes and noticing teeth decay in the upper and lower jaws near the nodes, he assure me that it is nothing more than inflection from the decayed teeth and cold that caused him before and there is no need to worried about. but again i was still worried about and after 10 days i took him to another doctor, he make a sonar and says that the lymph are normal but there is concentration of blood vessels near lymph, so it is nothing to worried about but medical follow up is recommended. later i decided to treat his decayed teeth in the left side and really after treatment i feel the node in the left is getting smaller and it can not be noticed even by touching easily but still not removed yet. the one in the right side, i feel it is bigger than the one in the left side but also hard to notice by touching and there is still decayed teeth in the upper and lower right jaw which is not treated yet. i do not know is there a concern about it or it is just infection and no more. what i am worried about is the long lasting of such nodes!!! pls help me with your advise