Even though California juvenile records are not sealed at 18 years of age. Are the records public information and show up on background checks?
In theory, your juvenile records are confidential and can only be disseminated in limited circumstances. Normally employers don't have access to those records, but if you are applying for law enforcement positions, a juvenile adjudication of theft may be discovered. Although record sealing is not automatic, it is certainly something that can be done after your juvenile probation has expired.
Normally they don't. Why don't you go through the process of having them sealed/expunged? That would be the best thing to do in this situation.
Good luck with your situation.