There's really no such thing as a 'rollover' to a 529 plan except from another 529 plan owned by the same individual.

Cash is the only contribution that can be made to a 529 plan, so the assets held in the UTMA would have to be sold first, which will be a taxable event to the children, with any investment income realized in excess of $1,800 to each child taxable at your tax rate.

And the 529 plans you establish would have to be titled to the children. Some states may have restrictions on custodial 529 plans, as the 529 is really a state regulated entity with Fed taxation rules held by the IRS. But moving assets from a custodial account to a 529 does not change ownership or who the funds are ultimately to benefit.

The benefit of doing this is tax deferral and possibly tax-free earnings if used for the children's qualified education expenses in the future.

The cost of doint this is loss of flexiblility in investments and loss of flexibility in what the funds will ultimatly be used for, without significant penalty.

BruceM