The way I understand it, animal fat IS good for them developmentally, but I would caution you to only serve them the fat from organic meats and poultry.
In non-organic meats and poultry, the injected hormones and antibiotics they treat the animals with tend to accumulate in the fatty tissue, so that part of the meat is actually very unhealthy for children (and adults!) to eat.
HTH,
Suzi