Underflow in the root of a B-Tree

I am trying to implement a 3-4-5-6 Tree. In the event that a merge causes the root to have only one key (underflow) and its children have a total number of key greater than 5 (so if all m开发者_开发技巧erged together, an underflow would happen), what should happen?

Split the children of the root up so that you end up with a "legal" root node and two "legal" children.