If I'm claiming my nephew do I need to have a form like 8332 or 8453 ?

Neither.  The form 8332 is for the release of the exemption by the custodial parent to the non-custodial parent.  Form 8453 is the transmittal form for a efiled tax return.  Here are the rules to determine if he would be a qualifying child for the $2000 child tax credit.

Generally, a taxpayer will receive a $2,000 tax credit for each Qualifying child claimed as a dependent on their tax return, subject to certain income limitations.  To claim the Child Tax Credit or Additional Child Tax Credit, the taxpayer (and spouse if filing jointly) must have a Social Security Number (SSN) or individual taxpayer identification number (ITIN) by the tax filing due date of the return (including extensions). Any child used to claim the credit must also have an SSN valid for employment issued by the due date of the return (including extensions).

The child must meet the following eight requirements to be considered a qualifying child for the Child Tax Credit:

•  Is the taxpayer’s son, daughter, stepchild, foster child, sibling, stepsibling, half-brother, half-sister, or a descendent of any of them (grandchild, niece, nephew, etc.)
• Lived with the taxpayer for more than half of the year
• Was under age 17 at the end of the year
• Did not provide over half of his or her own support during the year
• Is a U.S. citizen, U.S. national, or U.S. resident alien (child tax credits are not allowed for nonresident alien children residing in Canada or Mexico even if they qualify as dependents)
• Is younger than the taxpayer claiming the child
• Does not file a joint tax return unless the return is filed to claim a refund and no tax liability would have existed had the child and spouse filed separately, and
• Is claimed as a dependent of the taxpayer claiming the Child Tax Credit