Bubble baths are not recommended for children that have sensitive skin, or are already prone to UTI's. Some experts say that children under three years should not have bubble baths at all. Individual bubble bath products differ and parents should familiarise themselves with the ingredients in each one they buy. Generally speaking, buy mild products that are designed for young children. It does not have to be the most expensive brand, but it should not contain too many chemical additives beyond what is needed to make bubbles.
Even soapy water can cause UTI's in children. There is a percentage of healthy bacteria present on a child's skin and if that bacteria is killed off, then infections are able to start and spread easily. As a precaution, mild child soap should be used and children must always be well rinsed off after bathing.