I wouldn't consider it prudent to encourage a youngster to mix electricity with water. No matter how safe this particular unit may be you are setting a precedent that electrical items are OK in a water environemt. It will difficult to teach her the difference between safe, well constructed, water certified eletronics and non-safe ones. The simple rule that electronics and water don't mix is easy for youngsters to understand and it may save your PDA and your youngster. When they are in 6'th grade and starting to learn the basics of electicity and waterproofness then it may be possible to enlighen them on how to make the distinction. There will be plenty of opportunities for your youngster to get ahold of portable electronics and submerge them in the sink without you noticing untill too late. You would be better off it htis entire category of experimentation is ruled out at the start.

Just my opinion as a father or two daughters (7 and 9) who have caused plenty of damage without this set of opportunities available to them.