What can I do if my girlfriend is keeping our kids away from me just to make me come back to her and there is no court order?

In order for you to get any rights to your children, you would have to pursue an action for paternity. Until that time, your girlfriend, by default, has all the rights (time-sharing rights) and decision-making authority over your children, including the right to keep them away from you. So I suggest that you move forward with a paternity action right away. Good luck.