The boys are always on board with new blankets, especially when the blankets are soft, warm and fuzzy.
I cut the king sized blanket straight down the middle. Then I grabbed two twin sized flat sheets that weren't really being used and cut them down to size. To finish I just sewed around the outer edge to stitch the sheet and blanket together. The two new blankets are slightly skinner than a twin sized blanket, but the boys are little and only really care that they get more new stuff.