Suddenly vacant robin nest

We’ve had robins nesting in a cubby hole in our garden wall for a while (a month and a bit, give or take) and a week or so ago they lay some eggs. They hatched into about 4/5 chicks. Our gardens pretty small, so they’ve been easy to spot and we’ve watched them, from a distance, gather worms, and other things for their chicks. Until a couple of days ago, they were still in the nest. A couple days ago, in the evening we checked to nest to see if we could see them and there was no sign of life there - it was completely empty. The nest was perfectly in tact, and wasn’t broken, and it’s pretty tucked away anyway so we have ruled out that they were eaten. Since then we haven’t seen them at all in the garden, or flying about like usual. However, we think we might have seen one of the chicks flying but we can’t be sure. I’m not a bird expert by any means so I was wondering what happened / if we did anything wrong? Thank you for your help!

( If the timings of the events seem a bit off, they probably are - I’m writing this with a failing memory Sweat smile