At that age they won't have an adult appetite yet. I'm sure before long they will learn to eat more.
Often my gliders come out after dark for a quick bite and then go back in the pouch. They don't really become active until after I go to bed, except for one who is always on the lookout for a treat!
When I first started using HPW, I was surprised that it melted down into a liquid, but they like it that way. I guess that's why they don't drink much water.