Unfortunately ankle and hand weights do not provide the best method to build bones.
a) Jonathan and Shay point out the drawback of weights that are too light;
the load is not enough to improve bone strength
b) Stephen and Michelle point out how the extra weight throws off a person’s
gait and can cause injuries.
The weighed vest idea may work (if the person has no back industries); the stress caused by heavy weight further from the center of the boy (i.e. on the ankle or in the hand).
(Resistance training would improve bone strength. However your client seems to be bent on walking; I’m not so sure how the client will respond to using weights.)