Hi, I'd like to help you with your question.
The best thing you can do for your children is to tell them the truth. You do not have to tell them that their mother is bad in order to do it.
Your kids are old enough to understand that some things are out of your control. Make it clear to them that you are fighting very hard to see them as often as possible. This lets them know you care for them and love them, but circumstances beyond your control have caused you to only be able to see them as often as the courts allow. Tell them that courts often work the best they can, but that the decisions are not always what each parent wants.
Also, tell them that with your physical disability, you need to get help outside the state. Let them know you still want to have contact as much as possible. If you are allowed to call them, let them know you will be contacting them on a regular basis to see how they are. And encourage them to call you as often as they want to. If you can, consider Skypeing each other. That way, you can share and see each other. You can talk about homework, activities and just enjoy talking face to face.
You can also send gifts. Kids like getting things in the mail so if you sent them packages, they will feel closer to you. You do not need to send expensive items. Simple things like stuffed animals they like or a computer game is nice. Anything that you know they like.
Let your kids ask questions. Keep the lines of communication open as possible. If they ask about your ex, keep your answers neutral. "Mom and I could not agree on that", or "We tried to find the best solution for everyone but sometimes it doesn't work that way" and the most important answer, "Mom and I both love you very much and that will never change". These types of answers help give the kids answers but also keep your feelings about your divorce from making them feel burdened or responsible.
Make sure the kids know that they are not responsible for anything that is going on. They need to know that sometimes adults can't get along and need to be apart.
As your children get older, they will understand more and more about the situation. Kids are smart (it sounds like your children especially!) so they know more than they let on. And as long as you stay in touch and reaffirm your love and concern for their well being, they will seek you out and want to maintain a relationship.
I hope this helps you,