I think that theft is so high because many youths have opportunities to thieve, rather than have opportunities to commit other crimes. Although theft is a less serious crime than, for example, a violent crime because people’s lives are not necessarily in danger during a theft, they are during a violent crime.
The “Youth Justice Statistics 2014/15” (regarding England and Wales), written by the “Youth Justice Board/Ministry of Justice” on the 28th of January 2016, it discusses, for example, movements through the Youth Justice System, proven offences by juveniles, and measures of crime underwent by juveniles. According to Youth Justice Board/Ministry of Justice, In England and Wales, in the year ending March 2015, the main types of juvenile offence were; violence against the person (24%), theft and handling (17%) and criminal damage (12%). Additionally, there were 2,000 sexual offences in the same year in which a young person was cautioned or convicted, which accounted for 2% of all juvenile offences.