Q: How do you know when it's appropriate to offer your child help/assistance?
A: When the offer feels inspired rather than fear-based.
If you're coming from a perspective that your child is helpless, damaged, weak, incompetent, lost, wrong, etc., then your "help" will only give power to that belief. It won't feel inspired to you, and it won't inspire your child to connect with his or her Power.
But if you consciously shift your perspective to one in which you see your child as capable of finding his or her way, you won't feel like you "should" help, and you probably won't offer to help unless asked.
However, you might be inspired to get involved in a way that doesn't feel like you're a "have" helping a "have-not" — it'll feel more like two souls playing together, co-creating purely for the joy of it!