According to some early guidelines mentioned by the state of California regarding a multi-phase plan to gradually reopen businesses in the state, it sounds like the opening of attractions that would normally contain huge groups of guests at one time may not reopen until the laser phases of the plan. This could potentially delay the reopening of big parks like Disneyland and Universal Studios Hollywood for several months.
While the subject of “theme parks” are never officially mentioned, this is the early thinking based on the first suggested guidelines. Of course, during the early days of social distancing, before stay-at-home orders, theme parks were going to be allowed to stay open at the time. So you never know, with the right proof of concept in place (like the successful reopening of parks elsewhere…) exceptions may be made and parks could open sooner.