Scarlett-Rose Davis, three, from Coalpool in Walsall, West Midlands, was shown taking the challenge in a video shared on YouTube.
The little girl divided opinion with her 'F***ing hell' comment after the water was tipped over her head, with some people seeing the funny side – and some not so much.
Now, Scarlett-Rose's grandmother, Carla Davis-Bell, 40, has spoken about the clip - and her granddaughter's colourful language.
"I couldn't believe it when she came out with that language. She has picked up a few bad words when we have gone out for meals or into town," said Carla, who recorded the footage with her husband, Stuart.
"It did shock me but she's so clever I'm not surprised she's picked it up. We told her it was a naughty word. Children have brains like sponges and I can't stop it. But she does know it's wrong.
"I have to say when I heard her swearing I nearly died with laughter. I know it's wrong but it's the same reaction most adults would have after being drenched in ice water. We did tell her not to say rude words and she is normally very good and polite."
Scarlett-Rose was desperate to take part in the challenge, and Carla and Stuart only agreed if they could use warm water.
"She had seen some of the ice bucket videos on my phone and seen one of my friends do it," added Carla.
"She said: "Nanny, can I do that?'
"I wasn't keen on her having ice water poured over her so I said we'd use warm water from the cooking pot. It makes me so happy that a three-year-old picked on a good cause and wanted to get involved. She knows it's for poorly people."
Scarlett Rose's mum Demi, 19, added: "The reaction to the video has blown my mind. My phone is on charge constantly because of all the comments have received."
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