Thanks both! I don't think the fox will try and get in. The run has an outward skirt to try and prevent them, the run will be kept relatively close to the house and I've not (yet) had a problem with foxes trying to dig into the poultry runs. But at least if they're shut in at night, they should be marginally safer (and out of temptation). Good plan to train them back in with food.
I had pet rabbits (Netherland Dwarfs) as a child and don't remember them ever trying to dig out but we did move their run daily. We'll just have to deal with their digging by moving their run more often and if they do dig seriously, I could put the run on top of chicken wire but would rather not.
I hadn't thought of the specific foods - hmm, good point. I'll have to ponder that one. Son won't try and catch the quail - he'll be rabbit focused. But I imagine they still scare easily. Maybe if I get lots of cover for them? They're really hard to shut up at night, aren't they?