I do believe that people who have a stable childhood will grow up to have a stable adulthood. Childhood shapes an individual's character, and who they become is very similar to the same person they have always been. People don't change much throughout life, unless something traumatizing has happened, in which case a person will accommodate those changes through the facts they knew before.
I completely agree with this. The stability of the environment in which a child develops plays a large part in shaping their character and the way they will handle themselves later on in life. We learn how to handle things usually by modeling them after our environments and also learn through experience. Our experiences shape us into the people we become later in life, in some way or another, whether we realize this or not. Past experiences teach us things and cause us to have slight changes in character, some more obvious than others. If something traumatic has happened during childhood, it is very likely that a person will be more guarded and may still be scarred by the experience later on in life, thus becoming less trusting in others and more guarded. The person may not have higher well-being later on in life, as their experience may limit them in achieving their potential and being open to new experiences and hinder their social lives. The person may be troubled greatly by such an experience and have a hard time adjusting later on in life, even if they did have secure attachment as an infant. Experiences and our environment shape the people we become and can affect our well-being greatly.