This is solved now!!
I had a call with TurboTax specialist and together we were able to find a solution here.
Actually the issue is, In Turbotax under the Child SSN field there is option which need to be selected if it is a ITIN. Though i had selected it for my daughter with ITIN number and did not selected for my son as he do not have the ITIN yet and i will be applying this year.
When i selected the radio button below the SSN field for my son without entering the SSN showed the correct $500 amount.
