Los Angeles County probation officials say they are now studying how other counties recover juvenile detention costs, after admitting they mistakenly billed parents for days when youths were held in probation camps and halls. By law, California counties can bill parents and legal guardians for some daily costs of detaining youths, but only those whose parents can afford to pay. Last year, more than 20,000 youths were admitted to probation camps and halls, and L.A. County billed parents a daily charge of $11.94 for camps, $23.63 for halls.