If a lesbian couple want me to help them conceive a child, can they or the state come after me for child support even if the three of us sign an agreement stating that they won't seek child support and I won't seek paternal rights.

See a lawyer and protect yourself. What you need to do is check the adoption laws for your area. That is what you want to do is allow for an adoption. In doing that it would release you from being a legal parent. If you do not then it could be overturned do to laws stating the child is suppose to have the benefit of both parents. By that you could owe child support and much more.

You would really need a lawyer to draw up that agreement. And depending on the state that might not even do it because in some states two women do not equal a mom and dad.