Beef mince, Sluis, waxworms. CLO mixed with water. Place them in a box on tissue paper or a towel with a hot water bottle under the box. Birds are better kept warm from above but this will do as a temporary measure, or they could be put in a box in an airing cupboard. Baby birds needs to have food put into their mouths, they will not pick up food left beside them.
Seed eaters have shorter round beaks.
Insect eaters have longer wider more pointed beaks. A young bird will probably open it's mouth to be fed but if not gently open the beak and pop the food in, pushing the food down. Water is given the same way on a paint brush or with an eye dropper. The liquid can easily collect in the lungs and cause pneumonia. If you are sure the bird is an insect eater raw mince or tinned cat food can be mixed in.