This is why all jugs and containers in kitchens and food service areas should be color-coded.

One-year-olds Daniel Martin and Sophie Watkinson were rushed to hospital with injuries to mouth and throat after their sippy cups were filled from unmarked jug containing pipe cleaning fluid instead of water at a Toby’s Carvery on Ecclesall Road South, Sheffield.

“When Daniel began to cough we were encouraging him to sip more water, which was obviously just making it worse,” said Mrs Martin, from Bury.

“At the same time, Stuart and myself took the lids off the children’s cups. I put it to my mouth and immediately it smelt like bleach.

“The barmaid came and said: ‘I’m really sorry, we’ve used the pipe fluid.’ I didn’t believe her at first.

“The manager called the ambulance and gave us a bottle of the cleaner to show us and to show to the doctors.”

Kathryn Baines, a public liability solicitor at Irwin Mitchell, said, “It beggars belief that this hazardous liquid was, as we understand it, left in a water jug without any warning or hazard signs to identify it.”

The restaurant chain, owned by leisure group Mitchells and Butlers, said staff have been retrained in cleaning practices following the incident in May.

A spokesman said, “We can confirm Toby Carvery has admitted liability and are currently in correspondence with Mr and Mrs Martin’s solicitors. The safety and well-being of our customers is our primary concern.”