Tax breaks available to taxpayers with children are:

1.  dependency exemption
2.  head of household filing status
3.  child tax credit
4.  child and dependent care credit
5.  earned income tax credit

But each of these used to have a different requirement for when a child qualified for favorable tax treatment.  Now the IRS has created a uniform definition of a qualifying child.  This was done to streamline the tax rules related to children and make the regulations more consistent.  There are still a few variations left.