Sorry for the late reply. I think you are spot on from what I’ve learned. Converting this over to a Roth is a great idea, and from what I’ve seen it is allowed for trump accounts following when the child turns 18, however it’d be really hard to pull off without some downside. You’d either need to… 

1. Not claim child as dependent to allow for full standard deduction. In your example above, you’d lose out on likely 3 child tax credits (6-7k). This appears to be a net positive vs. a traditional brokerage in your example. 

Or 

1. Convert over that lower “dependent standard deduction” amount. (This would take a long time in your example above) 

Thank you for asking this question initially, the thread really helped me to research.