Elizabeth Warren’s plan for providing child care to all U.S. families who want it would require the creation of a massive, highly qualified workforce for an occupation that already struggles to attract workers.

Advocates for universal child care aren’t sure precisely how many workers would be needed for the endeavor, but they know the U.S. already is facing a drastic worker shortage. One analysis, from the left-leaning Center for American Progress, found that half of families live in places with no available child care.