Baby robin

Hello,

we have a Robin nest in the garden but a neighbours cat has managed to find it and had one of the babies out. It seems to be unharmed but seems really young. I’ve put it in a “nest” as close to where I’ve seen mum and dad going into the hedge - but it’s dark now and worried it’ll get cold. I’ve tried to hide him and hope the cat doesn’t come back. 

I’ve watched the mum and dad and it seems they’re still looking around for it, is there anything else I can do? Photo of what I’ve put it in - popped some mown dry grass in the bottom