We should probably think of it in the other direction: Some will outgrow it, which is a likelihood we can express in relation to a certain age, statistically. This does mean it becomes ingrown and unable to change beyond that. Indeed, many stutterers will find it changing regardless of their efforts to change it or not. But the key point is probably that we should keep trying to change it, if it's causing us distress. "Support" depends on your kid, really. Use whichever resources you can (founded in professional settings, of course). Perhaps your kid will tell you or perhaps you'll have to help them in expressing it. I don't think there's a single solution, you know?...