Do I need any type of document to take my kids out of state for awhile?

I have been married 9 years and have two daughters. I am a stay at home mom for 2 years. I have no family here besides my husband and two daughters. We both are originally from another state. Recently, my husband told me he wants to get a divorce. We have one daughter of the 2 with health issues who sees a specialist every couple months. He says he will give me sole custody, child support, and spouse support. Basically whatever I want. I am going to go visit my parents and stay there until December. I am taking my daughters with me. Their father says it's ok no problem. Do I need documents to take my kids with me? Also we agreed that when we come back in December for my daughter’s doctor appointment, I would start packing and getting things ready for our divorce. I will be moving back to move in with my parents. Can I file for divorce, sole custody, child support, and spouse support while I am in another state and get everything I am asking for? Again, he says he will give me whatever I want. He says he will not fight me for anything.