Would things like blowing out through straws or kid blow toys help expand lungs and increase lung breathing capacity? other suggestive techniques ?

Hard to say: The short term effect of a kid blowing windmill toys or through a straw will permit them to expand their lung to its normal capacity. I use these in my office to aid listening for breath sounds.While this may help stir up mucous and allow them to cough deeper, the long term effect on vital capacity or airway efficiency is unpredictable. Healing of pre-existing problems promotes their return to nl.

Possibly helpful: Some evidence exists for using positive pressure or incentive spirometry to enhance lung capacity. Any deep breathing exercise or activity such as swimming or playing wind instruments may be helpful as well. JDF1⅝