Pediatric Physical Therapy published the results of a survey completed by 513 pediatric physical therapists who use support walkers. Support walkers were used most often to improve mobility, gait, participation at school and socialization with peers. In general, the devices were used for one month as a trial period before purchasing. This was followed by 9 sessions of training provided in the school. The researchers concluded "Pediatric physical therapists use SWs to increase postural control, mobility, and children's participation in school".
You can read more on this study over at Rifton where there is a nice summary of the study with more details regarding therapist's reasoning behind choosing support walkers.
Reference: Low, Sheryl A. PT, DPT, DSc, MPH, PCS; McCoy, Sarah Westcott PT, PhD; Beling, Janna PT, PhD; Adams, Janet PT, MS Pediatric Physical Therapists' Use of Support Walkers for Children With Disabilities: A Nationwide Survey. Pediatric Physical Therapy: Winter 2011 - Volume 23 - Issue 4 - p 381–389