As a martial art there can be some concern as to injury. A survey of the medical literature though shows that for children judo is one of the safer sports they can practice.
The table below is built from data in the two cited studies below. A little math done to make the numbers per 100 practices/games.
practice game soccer 0.5 1.8 per 100 baseball (boys) 0.6 2.4 per 100 martial arts 0.4 1.3 per 100
Compounded with the focus on safety that judo has putting it in the lower risk of all martial arts, in part represented by the low number of injuries in the martial arts category that are attributed to Judo.
Marirose A. Radelet, Scott M. Lephart, Elaine N. Rubinstein, Joseph B. Myers. “Survey of the Injury Rate for Children in Community Sports” Pediatrics September 2002, VOLUME 110 / ISSUE 3