Ken's been the object of his son's rejection. There are a couple of possibilities.
Preschoolers are emotionally unpredictable and have difficulty dividing their attention.
The next, Sara and Michelle play happily in the sandbox while David sits alone. In much the same way, as your preschooler attaches to and forms bonds with one parent, he may simultaneously boycott the other. Tomorrow, his choice may be reversed. Keep in mind also that behavior that's interpreted as rejection is often simply a child's attempt to promote her individuality and independence. Jump into the fray.