"Das Kind isst gern Reis."
If I had been asked to translate it, I would have gone with "The child likes to eat rice." "The child eats rice with pleasure" seems a little loose to me, but I could go with that. Ironically, the thing I can't go with is "The child is eating rice willingly." and that seems to be the "correct" answer. That seems like too much of a stretch to me. Eating it willingly doesn't mean he necessarily likes it, but the original German version does mean that he likes it.