Well, that is the premise the author has...one skill per year of age. (I was mostly teasing about the nursing...that's not one she mentions but it *is* a self-calming tool.
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There are six main types of self-calming tools, and that's in ch. 4, so stay tuned, lol, but some other examples would be comfort corner, watching swaying trees, large-body mvt's such as jumping or running, repetitve tactile things things like stringing beads or playing play-dough, drinking tea, warm bath, etc.