@gaby1254 before closing this out, let's be sure you got what you were entitied to:
1) if you received $4200 last spring but you now have a newborn, then you are entitled to $5600.
Therefore, Line 30 of your Form 1040 should be $1400.
Please be sure that whatever you actually had on the tax return LESS the IRS adjustment yields $1400.
