You do not need marriage to have kids.
Getting married is like taping a shotgun to your neck and putting the trigger in her hand. She can pull it any time you like and you can't put the bullet back in the gun.
If you need to have kids, negotiate with her, set up a parenting plan before the children are conceived, put metrics in there coupled to a burden of performance, having a legally binding agreement written up by an attorney will solve any issues you may have with family court because if she does file and try to take the kids from you, you already have an agreement.
Things I would include are that your children will always live in your home, if she is living in your home, you will be the only man in her life, if she decides to leave she will not bring other men around your children.
You have to take the upper hand.