First, such a wide crack could indicate structural problems. This needs checking and repair before proceeding.

To fix the cracks you have a couple of choices.

* Use a stucco patch compound. This is a cement based powder just like the original stucco. You might need to pre-fill the cracks then use fiberglass mesh tape to reenforce the cracked stucco. Cover the mesh tape with more patching compound then texture to blend.

* Open up the crack a little further using a Dremal or Roto Zip with a wide masonry bit. Apply bond breaker tape to the crack and patch using several layers of elastomeric stucco patch. Check with your local stucco supplier for the needed supplies.