Hello,
I have 17months old son, recently observed a smaller than pea sized lump delow both the ears on the neck.
He does not seam tohavepain or anything, and is absolutely normal.
I am sick worried ,can anyone tell what this could be ?

You should definitely get to your family physician as soon as you can. None of us here can diagnose your son. When my sister was a toddler, she had small lumps like you are describing. They may or may not be the same thing. Hers turned out to be cebacious cysts. They were drained and removed, and she was just fine, although they did keep on turning up periodically. See your Dr. and get a diagnosis.