It's great that you're helping your grandchildren!
You're making a rollover, it just happens to be in the same plan and to the same beneficiaries. Your plan provider should be able to help you with this. You can call the folks at T. Rowe at 888-463-4723 and they'll walk you through all the paperwork that will need to be completed to do so.
VP, Research & Development
This information does not constitute tax advice and is provided for informational purposes only. Please consult your tax advisor, financial advisor, local taxing authority, and/or plan provider or sponsor for more information.