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Single lymph node has no significance if there are no associated infections.
Maybe your child had some cold or minor infection around that area due to which the lymph nodes got enlarged.
You should show a doctor when lymph node increases in size as it is becoming very painful for the child, more numbers come
Else, it is absolutely safe and will disappear within a week or two. But if you are so concerned, they will suggest an ultrasound to rule out that it’s not infected or not a lymphadenitis.
For more information consult a paediatrician online -->https://www.icliniq.com/ask-a-doctor-online/paediatrician