What workup do you recommend for isolated postural and action tremors in a developmentally typical toddler?  

Rule out Wilson's Disease. 24-hour urine copper, ceruloplasmin, consider further testing, definitely monitor for progression of other symptoms.

I typically don’t do any workup for these kids especially if there is a family history of tremor. I advise them to see an OT if needed for weighted utensils, slant board, etc.