I had a child with at that time my boyfriend after we split up I had custody of my son who is 4 years old now when we were together we lived with his mother we split up and my ex boyfriend went to prison for 3 years I have been raising my child by myself when I moved from my ex's mothers house som personal papers were left behind I went to get the papers so I could file my taxes and my exs mother said she had already claimed my son on her taxes she has nothing to done nothing for my son what can I do

Prepare your own return and claim your child. Go to your ex's mother and say the following: "I have the legal right to claim my child on MY tax return under the Internal Revenue Code; you do NOT! When i file this return, the IRS will ask for proof from both of us that we can legally claim him on our respective. I have that proof; you do NOT! Do yourself a favor and AMEND your return to UNCLAIM my son. That way, you only lose the exemption and the Child Tax Credit. If the IRS determines that fraudulently claim my son on your return, the penalties and interest could easily DOUBLE what you would have to pay back."

If she does not listen to reason, file your own return. When the IRS contacts you, prove that you had custody of your son and were entitled to claim him, and what you quoted above WILL happen.