Help! Abandoned Great Tit Babies?

Hello, I was wondering if anyone could please give me some advice? We have been watching a pair of great tits in a nesting box with a camera for a while now and they have 6 babies (they’re about one week old now).

However we noticed yesterday afternoon that the parents hadn’t been to feed them for a while and it got dark and they still didn’t come. They weren’t back by midnight, I don’t know if they returned during the early hours of the morning but they definitely haven’t been back at all today either. We’ve seen some great tits flying around and heard then singing in our garden but we’re not sure if they’re the same ones.

I was just wondering if this is normal great tit behaviour? We had great tits in the box last year too but we don’t remember them leaving the babies alone for as long as this.  

I’ll leave some photos here:

They’re quite lethargic now. Only three of them are still lifting their heads, we’re very worried about the other three. Should we feed them? Any advice would be much appreciated. Thank you!