Babies and young children should not be allowed to drink mineral water, and baby formula feed should not be made up with natural mineral water. Some have high salt or high sulphur content and, in particular, a high uranium content. Uranium is a heavy metal that is toxic to the kidneys and liver. The radioactivity of natural mineral waters are generally too low to be problematic.
http://www.bbc.co.uk/dna/h2g2/A13745991