Cats poo in mulch ??? Using as a toilet

Place citrus peels,make citrus sprays,

I scattered pine cones in all my flower beds, and it solved the problem.

Unfortunately cats will poo where it is easiest for them. You would have the same problem if you have a sand pit or a freshly dug flower or vegie garden. If your do not have a sand pit for the kids you could try adding one in another location of the garden and continually take the cat to it and move its paws (safely) to replicate digging and maybe it will start using that area as it will be easy. Maybe placing some of their poo in the sand pit will work(?) but you will still need to show them. If they start using it you will still need to keep this area clean but sand is easy to clean up and it is not in the children's play area. In the mean time I would hose the cat every time you see it on the bark.

You could try placing a layer of chicken wire just below the mulch. It might work as it will be uncomfortable to their paws and again, "might" be a deterrent. Good luck!

Sprinkle cayenne pepper or chili powder in the area - You can get a large jar for a buck in the dollar store. This will not hurt the cats but they won't like it when they lick it off their paws - works like a charm

Spray some ammonia around the area. It won't take much, it might work.

Granulated moth balls

I have a machine with motion sensor. It can be dialed for small or large critters. A friend bought it for me 20yrs ago. Still works to keep neighbors cats from pooping in my flower pots. Not sure anymore where it was bought. Its called a Weltech pest repellent. Works with direct current or batteries. Im sure google would produce something similar. It makes high pitched sounds heard by animals.