What can be an alternative for pulmonary function test in kids when a kid is not able to preform the test with the right techniques?

You can get some, but not equal, information by having a kid "blow out a candle" or blow up a balloon. They may understand the process better using this analogy. Having try this function a few times they may be able to do some of the tests.

There are other methods including oscillometry available at some centers. At ages 6 or 7 years most children with practice and coaching will be able to compete the rest. Watch for signs of shortness of breath and response to inhaled medication.