I want to move back to Iowa to be closer to my family I have I have never been married to any of my kids fathers I need to know if I can leave state...

The only way that you would have to even consider letting them know is if you have put them on child support and you guys have joint custody... other than that you are not obligated to ask for any permission. However it might be a good idea to give them a heads up.

What does your child support order and/or the child custody order or child vistation order say about it.

Normally if you move you will need to get his permission or permission of the court. Esp if it states so in the court orders,

If it does not state it in court orders, you may try to move, but the father can file in court to have the children returned to his state pending a hearing.
** assuming you and he both still live in the same state