Is Glacier Shield Insulation warm enough (for a kid) even on a lightweight coat?

I have no personal experience. I think the hint is in the warmth to weight ratio it mentions i.e. it gives great warmth for its light weight (so a heavier coat may give greater warmth). An Amazon reviewer of Reebok Glazier shield insulation coats in America said 'Don’t expect a real warm jacket here, but for fall (autumn) days & cool spring nights, this is a trendy & stylish option'. Perhaps someone else has experience of using Reebok Glazier shield insulation coats in the Winter months.

If you're having doubts you already know the answer to the question.

From the info on the tag it doesn't sound like it will be the warmest option. If you're aiming for them to be as warm as possible in winter you should probably find something else. (edited)