Usually it takes six to eight weeks for a fractured leg or broken leg bone to heal. If the patient is elderly, their broken leg may naturally take longer to heal because of the aging process, loss of bone calcium etc..
A child's bones may heal even quicker than the six to eight week time period. And then other factors may be involved in the healing process. For example is the patient with a broken leg, or broken bones have Diabetes for example, or another underlying condition.
Such as being immunocompromised? Additional factors such as these have to also be taken into consideration and can greatly inhibit the body's natural healing process. Hope this helps answer your question a bit better.