Father, who is a banker, did not turn over our children's UTMA and UGMA"s when they became of age. What recourse do the have?

Divorced from a Banker, who had fiduciary responsibility to manage the money of the UTMA & UGMA accounts, in a prudent fashion for the benefit of our minor children at the time. When they became of age he did not turn over the accounts. There was a substantial amount of money in 6 different accounts. 3 opened by us & 3 opened by relatives. Since divorcing I have been acknowledged by the IRS as a victim of Identity Theft & Mortgage Fraud committed by my exspouse. He has comitted unscrupulous financial crimes, I do not want our children to be victims of this mans abhorrent behavior. He was supposed to protect and provide for his children not steal from them. I will do whatever's necessary to protect their rights and not allow him to control them by way of financial abuse. As a multi-millionaire he does not need our childrens money. How can they find out the status of there accounts & where there accounts are? What recourse do my 3 children have? He mentioned the money was spent to pay me support. I know this is not true. He habitually complains of having no money. I don't think he would tell his clients that.