Dead fledgling Blue Tit

Hi I am new to a lot of this and want to learn so much more. We have blue tits nesting in our air vent that goes in to the bathroom but luckily it’s not used often and when I saw them building the nest we stopped using the air vent... over the last several weeks I have heard the babies grow and it’s the most wonderful sound and sight watching the parents flying back and forth feeding them, such love and dedication !! However today I came home from work and went in to the garden and saw my cat acting strange and noticed that the blue tits ( mum and dad ) were flying low and also acting weird so I began to look further in to this and realised that they were looking at the ground ,I searched around and much to my fear there was a baby dead on the floor :-( this broke my heart to see and still breaks my heart. My concern is mum and dad are doing what’s natural in looking for baby and are trying to feed it but they don’t understand that it’s no longer with us.. what should I do with the little one ? Tears come to my eyes when I think about them , I’m so lost and feel so so sad for them ?! I can’t hear any other babies in the nest either .did they have more ? And have flown off ok? Please help if you can

thanks in advance 

Clare