Parents and teachers should take children's complaints seriously and not expect them to wait to go to the toilet, experts say.
A new NICE guideline was launched yesterday to "improve the diagnosis and care for children suffering with urinary tract infections (UTIs)."
UTIs affect some 82,000 children each year, and experts say it is important to diagnose and treat them quickly or else they can lead to permanent damage.
NHS guidance states: "In infants and very young children, the signs and symptoms of UTIs are often difficult to spot, so early detection depends on both parents and health professionals being vigilant."
NICE recommends infants younger than 3 months with suspected UTI should be referred immediately to a paediatric specialist and treated with intravenous antibiotic.
Andrew Dillon, chief executive at NICE and executive lead for the guideline, said: "This guideline will help improve the management of UTIs in children and babies by providing a handy guide to help health professionals diagnose the infection, outlining which treatments should be offered first, as well as explaining when further follow up or treatments may be needed.
"Parents will also be supported as the guideline highlights the importance of making decisions in partnership with their child's healthcare team."