Some call it a belly breath, others--a yoga breath; still more refer to it as a deep breath. Anyone under the age of 7 just call it breathing.
Right around age 7 we all go through a change. No, I'm not suggesting that's when puberty starts. What I am suggesting is that we somehow learn to breathe into our chest. Maybe it's a conscious (or subconscious) realization of our own waistline. I don't know.
What I do know, is that we become less efficient. In short: we work harder and gain tension!
This is what helps me: concentrating on taking in air, first filling the lower part of my lungs (pushing out your belly button) and continue inhaling until my chest rises too.
Better still: close my eyes and think a happy thought... well it's a theory anyway. I don't know, this rarely ever occurs to me, but it worked out for Peter Pan in Hook.