Kids typically produce the /ng/ sound between ages 2-3 . It is no longer considered developmental by age 4. Kids often make an /n/ sound instead of /ng/. When this happens, it is usually due to the back of the tongue not having enough strength to lift and form a seal. In this podcast, I talk about how /ng/ is produced, some methods to elicit the production, and how literacy and online resources will help to sustain it.
For more information, see my website:
https://vibespeechtherapy.com/