Stunting and underweight is usually a feeding issue. Either they aren't getting enough food or they aren't digesting it properly. When they aren't digesting it properly, it's generally because the food itself isn't appropriate (too hard or not moist enough, and in the case of handfeeding it might not be warm enough) or because there's a yeast infection or bacterial infection causing problems. The key to solving the problem is to figure out what's causing it and then do something to solve that problem. Susanne's websites have some excellent articles on dealing with stunting and crop problems, so I'd suggest that you go there and do some reading!
