This probably goes without saying, but it's important anyway. Keep your sense of humor. Remember the basics. However, they will eventually need to refer to their disability as well. Talk about the things that will be more difficult for your child.
Young children are naturally empathetic.
Will there be a transition buddy to help your child find areas away from the regular classroom. Don't forget safety issues This is a good time to build safety into the school day. Talk with the teacher about a normal school day routine. Be conscious of things like wheelchair safety, dietary restrictions, ambulation problems, or unsteadiness when walking. This may take some planning.