What should I need to do in order to move my children with me from non-custodial parent?

I recently got married and my husband is in the Military. He is stationed across the state from me in Texas. My children are not his. I am the custodial parent but I am not sure what I need to do in order to move my children with me. I did let the non-custodial parent know four months before my wedding that we would be moving, but it was not in writing. How do I approach this?