One measure of self-control is the ability to delay gratification; namely, the ability to wait in order to obtain a more valuable outcome in the future over a less valuable immediate one. In children, the capacity to delay gratification develops between the ages of three and five years old. In a new study, researchers used a rotating tray apparatus that allowed them to test both three- to five-year-old children and New Caledonian crows.

Read my post about it on my Animal Minds blog: Delay of Gratification in Kids and Crows.