What needs to be done in order to vacate my 15-year-old son's guilty plea? ?

My son pleaded guilty to felony lewdness with a minor when he was 13. He was helping his then 8-year-old brother adjust the water temperature in the shower. When my youngest son was asked "Has anyone ever seen your 'privates'" at school, he truthfully said that his older brother helps him turn on the shower. Because of their age difference (2 years or more in NV)they charged my older son as a offender! Our attorney told us to plead guilty, accept the required counseling and his record would be sealed after 2 years on probation. The state refused to administer a polygraph test on my older son because of his age at the time. Months went by, then he was placed in a mental health treatment facility out of state, where a polygraph was eventually given (he was 14). No surprise, he ped it completely. I also have a copy of a letter written by the state's offender counselor stating that in his professional opinion, my son is in no way a offender and never should have been charged. I don't want his records sealed, they could be UNSEALED. I wan't his guilty plea vacated. His probation officer admits she doesn't believe he is guilty! However she refused to set a hearing to allow me to speak to the judge (he doesn't know about the polygraph or the letter from the counselor). We don't have a juvenile public defender because we were represented by a private attorney who is no longer working on the case, for obvious reasons. The JPD's office won't ign us a JPD unless there is a court date, even though the court date request is exactly why we need a JPD. Please help!