I suggest that you delete Form 8615, then go through the entire Step-by-Step interview for Child's Income again from the beginning. Make sure you go through the entire sequence of questions, until you get back to "Your 2025 Income Summary." It will give you screens to enter all of the necessary information. You should not have to make any entries in forms mode.
If that doesn't work, make sure you do not have any overrides anywhere in your tax return. An override can cause the TurboTax calculations to break in unexpected ways, even if the override is in a place that does not seem to be related to the problem.