Don't worry about them regressing in school. Every single child is in this boat and they will be ok. When we are back in the classroom, we will of course meet them where they are. Teachers are experts at this! Don't battle if the can't do maths, don't worry about not following a schedule. Don't mandate 2 hours of learning time if they are resisting it.
If I can leave you with one thing, it's this: at the end of all this, your child's mental health will be more important than their academic skills. And how they have felt during this time will stay with them long after the memory of what they did. So keep that in mind, every single day.