ILLNESS
Tiny Tim suffered from an illness that made him weak, as indicated by references to his lightness and the family's concern for his health.
TINY TIM
'The colour hurts my eyes,' she said. The colour? Ah, poor Tiny Tim! 'They're better now again,' said Cratchit's wife. 'It makes them weak by candle-light; and I wouldn't show weak eyes to your father when he comes home for the world. It must be near his time.' ... 'I have known him walk with--I have known him walk with Tiny Tim upon his shoulder very fast indeed.' 'And so have I,' cried Peter. 'Often.' 'And so have I,' exclaimed another. So had all. 'But he was very light to carry,' she resumed, intent upon her work, 'and his father loved him so, that it was no trouble, no trouble.'