No, if two eleven-year-old friends, a boy and a girl, go out to dinner together with their parents, it does not count as a date. At that age, children often engage in friendly activities and outings with their friends, and it's quite common for parents to be involved in supervising and arranging such social interactions.
A "date" typically implies a romantic or potentially romantic outing between two people who have mutual romantic interests in each other. Eleven-year-olds are generally too young to be engaging in romantic dating relationships.
In this scenario, the dinner outing is more likely a friendly gathering, and the children are simply enjoying each other's company as friends while being supervised by their parents. Such social interactions at a young age can help build friendships and social skills without the added complexity of romantic relationships.