First Egg Hatching to Chicks Fledging - 21 days in 21 mins - BlueTit nest box camera highlights 2021

As you'll see, several of the chicks didn't survive to fledging. There was a cold snap during the nesting period which could have had a bearing on the matter. Rest assured that the bird feeders were (and still are) well stocked. Like minded people with bluetit nest boxes in the UK left comments saying many of their chicks also hadn't survived through to fledging this year either.
The chicks hatched over a four day period, usually this would only be a two day affair. The final chick to hatch on day 4 didn't stand much of a chance compared to its siblings which were already much larger after 2 or 3 days of being fed.

The sharper eyed amongst you might have noticed that there isn't a day 15 or 19 in the video. This was due to a recording failure and a computer meltdown. The camera and computer had been streaming 24/7 for two and a half months and started to fight back!

The parents continue to feed the chicks in and around the garden and the chicks have not returned to the nest box. This is absolutely normal.
The white fluff in the nest is Sheep's wool.