Its a difficult one and something I have not experienced with a broody, so if you get better advice, do follow it! Chicks will normally be fine for up to 48 hours (actually I have read its 3 days, but I was taught 24-48 hours) because they have absorbed the nutrients from the egg yolk, so I wouldn't worry unduly till 48 hours has passed. However, they do obviously need food and water. It is often said that broodies know best, but equally we also know that some broodies are just not cut out for it, although this often presents as aggression rather than neglect. And it is quite possible that the chicks have been fed/watered whilst you weren't looking, they eat so little at the start that you won't be able to tell from monitoring the feeder/drinker. Added to which, chicks do definitely need to be kept warm, so under Mum is the best place to be. I guess it is also possible that one or more eggs has not hatched so Mum might still be sitting tight for them.
All in all, I would not interfere yet, but continue to observe closely. It is more likely than not that everything is OK. I think many people would advise you to let well alone, but personally I believe good observation is the key to good stockpersonship and chicks are pretty helpless. So, if nothing has happened by the time 48 hours is up then I might try to guide the chicks to the food/water and dip their beaks in, so they know what the food and drink are. To do this you will probably have to remove Mum for a few minutes, but you need to make sure the chicks don't chill so act fast. I presume the food/drink is very close to Mum so she can get to it easily and show her brood what to do?