Robins nesting

Hi, can anyone help, I have some small 5 ft conifers that a pair of robins have nested in, they have been feeding the chicks constantly and can be heard each time the male or female returns with food, this went on daily for a couple of weeks, but suddenly all has gone quiet, I’ve not seen or heard them for a few days or so, what could be the cause of this, ?
I don’t want to poke my head in, just in case they are sitting quiet, I’m just a little fearful something has happened.