If parental rights were voluntarily terminated, can the state take any future children away from the parents

It depends on the circumstances around the termination. Generally the answer is no, because otherwise all birthparents who chose adoption for their child would be at risk for losing future children.

What were the circumstances surrounding the termination, and where are you located? The answer is going to depend on that information.

First it is VERY rare that parental rights are terminated, voluntarily or otherwise. Generally this is only done to allow the child to be adopted. Allowing an adoption is not likely to affect future children.

As noted, the real circumstances here have a major impact on the answer to your question. So if you want our help you need to give more details. Also ANY question on law needs to include your general locale as laws vary by area.

Were children's services involved?