She will go after the cats if they try, but no guarantee she can protect them, if they should wander away from her.. Typically both will stay put with the mother, but things happen. I have one duckling that chases bumblebees, and then peeps loudly because he gets "lost"! My barn cat fortunately knows all birds are hands off and usually hangs out by the coops.
She isn't letting anything near them. Unfortunately she is taking them out of my fence. They can go through the chain link and she can't. She has angel wing so flying is out of the question. Yesterday evening when I got them back in one was moving slow and having trouble keeping up. At lock up I found that sane one stuck between the duck house and the bantam coop. I a 2inch crack with wire on both sides. I got him out and he was cold. I put him in the brooder with the turkey poults she hatched for the night to warm up. Going out now to check on it.
Happy Mothers Day.