Get your taxes done using TurboTax

So you enter all four children in your tax return.  For two of them, you will indicate you have a custody agreement and the other parent is claiming the children (but be sure to say they lived with you all year).

You asked how to "amend".  Did you already file your tax return?  Is the original tax return wrong?  If so, this link shows how to amend your tax return:
<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed"...>