Why would you want to thicken them out for, strength gain or cosmetic gain? or both?
The wrist doesn't really have any muscle in it, its bone and tendins, so there isn't alot you could do about it other than putting on fat.
You can increase your forearm size however, and wrist curls can increase the strength in your wrists, along with grip strengthening equipment that can have an impact on strength in that region of the body.
Ankles - again just working the muscles around this region vastly improves the overall strength, such as the calf area. calf raises and squatting is good for this.