A new study has cast doubt on claims that all probiotic products can help a child's diet and nutrition by treating diarrhoea.
Probiotics contain microorganisms that can have a beneficial effect on health when they settle in the bowel.
But a study published on bmj.com has found that not all of the treatments are effective at easing upset stomachs.
Researchers at the University of Naples tested different products on 571 children with acute diarrhoea.
All the youngsters were aged three to 36 months, and were given popular brands or a control solution to simply rehydrate them.
The scientists checked the frequency of diarrhoea and monitored the patients for vomiting and fever.
Diarrhoea was "significantly" reduced in children receiving a probiotic, Lactobacillus GG - which is found in certain cures for digestive problems - and a mix of four bacterial strains than in patients receiving liquids alone.
But three other probiotics had no significant effect.
The authors said: "These results suggest that not all commercially available probiotic preparations are effective in children with acute diarrhoea.
"The effectiveness of Lactobacillus GG was not unexpected as several previous studies have shown similar results."
They concluded: "The efficacy of probiotic preparations for the treatment of acute diarrhoea in children is related to the individual strains of bacteria, and physicians should choose preparations based on effectiveness data."