When you're not married but want to start a family, you need to take steps to protect the integrity of your family unit. Fathers, in particular, must take special steps to guarantee their parental rights in Ohio. When they are not married, there is no assumption that they are the father of a child (after all, the only obvious biological parent would be the mother).
When any child is born out of wedlock, it's a very good idea for fathers to take steps to establish paternity. Even if the mother agrees that this is your child, you should make sure you are the one acknowledging paternity. If there is any question of paternity, get a DNA test to prove that you are the father of your child.
Is it a good idea to have kids without getting married?
Legally speaking, it can be a little more complicated than having kids when you are married, just because there is no assumption of a father's paternity at the time of a baby's birth. When you're not married, a mother could give birth and even go as far as to give the child up for adoption without informing the biological father. Whether that's legal is dependent on a variety of factors involved in the case.
It may be a better idea to tie the knot before having kids, even if it's just in a courthouse, because of the protections it provides you as a father. You will have all the rights and responsibilities that the mother of your child has, but you will potentially have fewer problems asserting those rights.
There is also the idea of child support. Men could end up paying child support even when they're in a relationship that would be considered similar to a marriage. To avoid a support order, getting married may be an option.
Overall, men who are hoping to have families with their girlfriends are at a slight disadvantage legally speaking. That's why it's usually a good idea to talk to an attorney before you start a family. If a marriage is a better choice for you, a simple document and a few hours out of your life is all it would take to give you the same rights to your children as the mothers who give birth to them. Marriage isn't a necessity, but it can certainly help protect your rights as a father.