On March 15th, Inslee announced that all WA public schools are required to have in-person learning options available for children up to 5th grade by April 5th, at least two days per week. All schools must offer at least two days per week to all students k-12 by April 19th. This does not change any of the health and safety requirements that they must meet. https://www.governor.wa.gov/news-media/inslee-signs-emergency-proclamation-requiring-person-education-opportunities-public-k-12
Helpfully, on March 19th, the CDC announced that physical distancing guidelines for k-12 students were being reduced to 3 feet in most cases where mask use is universal, except for middle/high schools in areas of high infection.