Newbie with questions

Hi. I am new to owning piggies. I got 2 guinea pigs from 2 different people who could no longer take care of them. I got them as classroom pets. My students love them and they get lots of attention. We started out with a cage that was too small. We have had our piggies for a little over a month and just built them a new C&C cage. They have so much more room. We are going to be adding a 2nd level in the next few days. We are waiting for the coroplast to arrive. My main concern right now is neither 1 will eat veggies or fruits. I have tried different kinds of lettuce, tomatoes, carrots, cucumber, green orange yellow and red bell peppers, apples....but they won't even touch them. I have continued totry them on several occasions since w got the over a month ago. NO LUCK! They get plenty go pellets and Timothy hay and eat that well....how can I get them to eat fruits or veggies? Am I doing something wrong? Not sur of their ages....but I think 1 is about 7 months old and the other is probably around 1. Should I be concerned or am I just being over concerned? Thanks for your help.