Children of unmarried parents have most of the same legal rights as children of married parents.
You can leave your property to anyone you want in a will, trust, joint ownership device, or other estate planning device. (See the Estate Planning section of the Nolo website for complete details.) In short, you don't have to sign a paternity statement or raise a child to leave the child property. But to be sure your child is provided for after your death, you do need to affirmatively leave property in your will or by use of a trust. This is because if a parent of an illegitimate child dies without a will, most states do not protect the child's right of inheritance as strongly as if the child were born to married parents or otherwise legally legitimated. For example, in some states, in the absence of a will or trust, the child can fully inherit from the mother but not from an unmarried father. Even in states that allow illegitimate children to inherit from a father in the absence of a will, the time in which the child can make a claim against the father's estate may be limited.
In the case of Trimble v. Gordon, 430 U.S. 762 (1977), the Supreme Court made it clear that a father's signing a paternity statement will normally be adequate to fully protect the inheritance rights of children born out of wedlock if there's no will. If your state rules allow a father to acknowledge paternity for the purpose of inheritance in a way other than a paternity statement, that will also be sufficient. For example, in some states, in the absence of a will, a child can inherit if the father admitted paternity prior to his death or if paternity was determined by a court. But obviously, a child's legal right to go to court to try and claim a share of an estate is not nearly as advantageous as being left property under the terms of a will. Or to put this point bluntly, if you want a child to inherit regardless of the child's legitimacy under your state's laws, accomplish this by leaving the child property in your will or other estate planning device.See the article Wills and Estate Planning for Unmarried Couples on this website, which explains how and why unmarried couples should prepare to protect each other and their children.
If a parent becomes disabled or dies, the person's biological or legal child may be entitled to receive income, such as from Social Security, government or pension benefits, or possibly a private insurance company (life insurance). In the past, benefits derived through the father were often unavailable to or reduced for "illegitimate" children—children born "out of wedlock." For example, Social Security regulations used to grant more benefits to the legitimate child of a deceased, retired, or disabled father than to an illegitimate child.
However, the U.S. Supreme Court has long since ruled that treating children differently on this basis is unconstitutional. It no longer makes any difference whether a child is "legitimate" or "illegitimate" for purposes of receiving Social Security and similar government benefits.
When it comes to private benefits, children of unmarried couples are similarly protected in most instances. For example, if you name your children as the beneficiaries of a life insurance policy, they will receive the policy proceeds if you die while the policy is in effect, whether you're married to their other parent or not.
Even though the legal rights of children born outside of marriage have greatly improved, that's not a reason for a father to fail to take steps to further protect them. The best way to do this is to sign a paternity or parenthood statement right away when your child is born. If you die, and you have failed to sign such a statement or otherwise clearly form a parent-child relationship with your child, Social Security or other federal, state, or private benefits may be denied your child because there's no proof that you were the father.