I'm I able to claim myself and my son as allowance on my W4?

Yes, you can claim 2 allowances on your W-4. Your U.S. Tax Return: Filing W4 Employee's Withholding Allowance Certificate

Actually, if you are filing Head f Household, you can claim up to THREE allowances on the W-4.

If you own a house on which you are paying a mortgage, the allowance can be upped to FOUR.

Right! as HOH, you can add “1” on line 'E".