Be flexible with time. Leave ample time to complete a recipe because you do not want to rush it.
Be flexible with cleanliness. Spills and messes are inevitable when cooking with kids. Using bigger bowls then necessary for mixing helps to prevent spills.
Be flexible with the end result. It is more the experience of the process than the end result.
Start with a clean and clear work space.
Have all the ingredients and tools out and ready.
Make sure your child can see and participate.
Talk about what you are doing. This is how to teach.
Keep it simple.
Involve your children in the clean-up.