6-12 children get childhood traits. Picking a certain focus makes it more likely that a child will get traits associated with that focus. 12-16 childhood traits randomly develop into one out of three regular adult traits. When a childhood trait turns into an adult trait the guardian may get an option to intervene and replace the newly developed adult trait with a trait of their own.
To give a specific example, let's say you give a child the Struggle focus at age 6 and by age 12 the child developed Rowdy. Then between ages 12 and 16 the child's Rowdy trait will randomly develop into one of the following traits: Dull, Honest, or Robust. For the sake of the example, let's say Rowdy develops into Dull. If the child's guardian has Brave they will now have the option to override Dull and replace it with Brave. So the child ends up with Brave instead of Dull.