A lot of people right now under the ruble. The theater was a standalone easy identifiable building, and it was known for days by everybody on both sides that there is large number or people sheltering there. Video from inside the theater before the bombing
https://www.youtube.com/watch?v=BVsEyYgenbU , and this is what they were sheltering from - Mariupol destruction
https://youtu.be/UqdS-T3l_fc?t=38.