Child hold his breath when talking.

[MuteDS]

I think I am sure his issue. When he sings, talk long sentences or blow balloons , he breath from his mouth and hold his breathing from nose ?
it’s cause issue for him like gagging or burping. I am not sure how to describe this behaviour?

A speech therapist could possibly help.

it sounds completely normal. You literally can't talk if you're holding your breath and you can't blow up a balloon with your mouth if you're breathing through your nose. Burping can be due to swallowing air.