Your girlfriend's 7 year old does not qualify you for a Child Tax Credit or Earned Income Credit or for Head of Household, because he is not related to you and cannot be claimed as a child dependent by you at all but as an "Other" type of dependent, if you meet those qualifications. Either you or your girlfriend can claim the younger child but only one of you can claim anything related to that child, such as Head of Household status, dependent, and any child related credits. You and the mother may not split anything related to that child between you.
