When do I worry about chick not eating

I have four "day" old (bantam chicks) from the feed store that I've put under our broody. Three will eat and drink (a tiny bit) but one wanders over to the food and water, but doesn't touch it, and then tries to worm it's way back under mom (who by the way seems to be a very gentle mother). How long can they go before they need much sustenance? The Silkie hen seems quite content to cover her brood quite near to the food and water so they don't have far to go for future 'outings'. My first chicks were given to me after they were a week old and otherwise most of my babies have been ducklings who have seemed quite robust almost immediately. Will the little reluctant one gain a little strength over night? Or will I need to try to do something to encourage it to eat.

 

Thank you! I just needed a bit of reassurance.