I think there is always an adjustment that comes with change in management, even within a family. Even without the learning curves that such an event causes, businesses will constantly have their ups and downs. However, the Trump family is famously wealthy, and I would imagine that their second-generation business will not have the struggles that an average-sized family business does. In fact, it does not really make sense to compare the two.
Yes, second generation family businesses struggle sometimes. Perhaps it is because the next generation doesn't have the same passion the original owners did. Maybe the businesses just outlive their demand among consumers. Either way, Trump's business is not necessarily doomed to fail simply because it has been passed down to the second generation.
Second generation family businesses often struggle. There are many reasons that a business can run into difficulties after the kids take over. Firstly, the original owner had a deep connection to building the business. The kids often grew up relatively affluent, or better off then their parents did. This can cause children to be less motivated to work hard. Finally, a changing business climate often means that an older business may not be as successful.
No, second-generation family businesses do not struggle because the younger generation had a lot of time to learn. The person taking over has a long history of being able to watch how the business is run. They know more about how the business runs than any other person possibly could in that role.