Did you try live? Mouse fuzzies, crawlers, or hoppers? Even mouse weans? What bedding were they on? (Many babies feel more secure, and so eat better, on aspen or cypress.) Did they have hide boxes?
Assist feeding a last resort. When its behavior around a variety of food items tells me it doesn't understand what food is/how to eat, and, more importantly, its body condition is going down hill - an energetic baby that seems like it could still take on live prey is not in dire need. (Also, just to clarify, condition and energy level are the main things I look for. I felt like I had to mention the behavior, because it has seemed like that can take a while to click in some babies.)