To CLAIM the child and all the child related credits then simply paper file a return with the child on it. That will get the IRS attention and both of you will get a letter in the next couple of years so be prepared to defend your position that you have the right to claim the child.
For details see:
http://taxes.about.com/od/dependents/qt/Dependents-Audits.htm
https://www.irs.gov/pub/irs-pdf/f886hdep.pdf
https://www.thebalance.com/claiming-same-dependent-audit-risk-3193030
