Just make sure there is enough bedding for them to keep warm, the mother will have made a nest using bedding plus her own fur. Don't be tempted to peep at them, leave them alone. Just ensure that you quickly put the food in and then leave (try to pick her some dandelions or sow thistle as this helps her milk, she also needs hay).
If you bother her by trying to look at the babies or touch them, she WILL eat them.
Wait until they are making their way into the living area under their own steam, it's then safe to pick them up and generally admire them.