I don't have my sons social security number

If you file your return claiming your son as a dependent and don't provide his social security number (SSN) on your return, the IRS will not allow you to claim him as a dependent.

Why would you not have your child's SSN?   If you lost the SS card then you might need to get a repayment from the SSA.   That might require you to visit a local SSA office with the child's birth certificate.  Call the SSA for guidance.