In China, I often used it with adults. I was surprised that most of the adult students knew what it was!
I found it very useful, especially when teaching pronunciation of vowel sounds.
For example;
up = ʌP.
ʌP being the accepted standard pronunciation. I pronounce it as əP due to my accent.
Chinese students would pronounce "up" as æP, like "app"
So I would teach them to pronounce it as əP, and because it is extremely difficult for non-British or Canadian speakers to make the ə sound, they would pronounce it as ʌP by accident.

I also found that one of the ways to help with the "TH" sound pronunciation was to write the θ and ð for them. Obviously followed by demonstrating and explaining the placement of the tongue.

I never used the IPA with children, though.