To find your biological children that went into foster care, you can use websites that are geared towards finding people online. Some of these sites include intellius.com, zabasearch.com and pipl.com. You can also try and find them by signing up with a reunion registry.
All of the above, plus i should think the state would have to give you info, no matter what the custody arrangement was; i think the goal these days is to keep folks together as much as possible. I'll pray for the best outcome for you all.
You won't find out believe me. They are protected in foster care. If you feel you have a case, go to the Department of Human Services in Oklahoma City, Oklahoma. They will decide from there. However, be prepared for all sorts of things to happen once they find out the where you are. But this is the main hub, in Oklahoma City.