I agree that you should start out smaller. If the children are very young they need something small enough to be able to drag around. If they are teens a twin size would be great for them to take away to college or their first apartment. After 911 I made three memory quilts for a family whose father was killed in the towers. Their mother sent me pictures of them with their father and items of his clothing. I made fabric photo tranfers of the pictures and incorportated pieces of the clothins into each lap size quilt. I also made each child a throw size pillow with a picture of them and their father on it. There were other quilters nationwide doing similar projects.
If you try and make king size quilts for each of the children you will burn yourself out and may end up wasting a lot of time and money.