You can file IRS form 3949-A (<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-pdf/f3949a.pdf">https://www.irs.gov/pub/irs-pdf/f3949a.pdf</a>) or call 1-800-829-0433.
But, quite frankly, doing it that way that doesn't make sense. If you are entitled to claim the child, you should go ahead and do so (see the recommended answer above). That's the best way to get the IRS involved. Any other method will be down played by the IRS as a family squabble
