I've recently found out that my 13 and 14 year old have had their last names changed for years now. How can I find out if they were adopted and when, because I'm still paying child support

How do you know it's a legal change? The custodial parent could just be having them use a different name. Also how did you find this out.

It is highly unlikely that anything legal was done, since you would have had to agree to it. But to check, you can check with the court where they live to see if any adoption or name change proceedings were done. Also check with the bureau of vital records where they were born to see what their official birth certificates say.

If you are paying support through a state agency, were you ever in arrears? If so, support would continue, even if your obligation had ended through an adoption.