If the breeder didn't introduce grass to the babies, then you will have to spend your time doing it. Hay is more for older ones. I start to introduce dry grass hay when they are around 12".
Chop up the day's greens into small pieces and spray with some water. Then chop up a tiny amount of soft, newly sprouted grass and mix it in thoroughly. When I say a tiny amount, I mean about 2-5% compared to 95-98% of their usual food. If the tortoise refuses to eat it, soak the tortoise and feed it the same mixture for the next day or two. A hungry tortoise will not be a picky tortoise. Over time, gradually increase the ratio of new food to old.