Which musical notation should be taught to kids first- the solfege (movable do, in this case) or absolute notation?
It seems that culture may come in here. In some countries, the solfege system is thought of as quite important. In France, for example, it's a fixed doh at C, and all the notes are named from this. So there, it would be useful. In England, there's not so much emphasis, so learning dots makes more sense. No doubt, other countries will have their own views, so the solution will vary. Best to go with the flow.
The fixed doh is not easy to sing with # and b. The movable doh will give some sense of key and intervals, but the stave is universal. For a child beginner it's pretty boring, though.