try feeding the bird on its own as i also have a young bird that only eats small corn, i noticed he wasnt eating bigger corns, so originaly i was feeding him larger corn by hand, but now give him a good handful of food on his own by the side of the loft, before all the others are called in, now he is starting to eat the larger corns, so for me was worth pursavering with, so i would possible feed him more by hand till he is eating more on his own, as for the watery droppings it could just be that he is not eating enough and drinking to much..