If the child isn't potty trained, you shouldn't put the child into any public pool, no matter what they are wearing.
It's very unhealthy for eveyone else. Read this CDC web page:
Are noroviruses contagious?
Noroviruses are very contagious and can spread easily from person to person. Both stool and vomit are infectious. Particular care should be taken with young children in diapers who may have diarrhea.
How long are people contagious?
People infected with norovirus are contagious from the moment they begin feeling ill to at least 3 days after recovery. Some people may be contagious for as long as 2 weeks after recovery. Therefore, it is particularly important for people to use good handwashing and other hygienic practices after they have recently recovered from norovirus illness.
There's a reason for the rule! I highly recommend following this rule.
Instead, pack a small blow up wadding pool for your child.