Remove the skin from the chicken and strip the meat from the bones; coarsely chop and put into a mixing bowl. Add the yogurt, grapes and celery. Mix well, season with salt and pepper, and stir until combined.
Lay the wraps on a work surface. Put 1/4 of the chicken salad on the bottom third of each tortilla. Fold the bottom up over the salad and fold in the sides, while rolling the tortilla up to enclose the filling.
Wrap tightly in plastic wrap or parchment paper until ready to serve. Refrigerate if not using before 2 hours.
These wraps are kid-sized. If you are packing a lunch for bigger appetites, divide the chicken salad between just 2 tortillas and enclose.