Blue tits gone

I hope someone can put my mind at ease!

Yesterday up until about 7pm or so the parents were in and out of the nest box all day feeding their blue tit chicks. Today... Nothing. Not a sign of any activity in or around the box.

Last year, exactly to the day, the chicks were in the garden while the parents still fed them but I hear and see nothing this year.

I fear something may have happened to them overnight or early this morning. Does anyone have any thoughts?

Thank you.