It could just be that they are slowing down for the year. Their natural clocks are telling them to slow down and reserve energy. Being young they probably won't go through a deep brumation but they will slow down a bit. As long as your temps and all that good stuff are where they should be, I wouldn't panic.
Keep offering them food and water daily but expect to see a slight decrease in consumption. They'll probably just nibble on things for a while until they "wake up".
Let us know how they are doing in a couple weeks.