(1) The best way to answer it to a kid is that basically, ice is lighter than water. Similarly, she can also say that the water is heavier than ice. We know of course that it has to be density; however, it will be much more difficult to refer to it as density to a kid.
(2) The type of bond that holds water molecules together is hydrogen bonding.
(3) When water freezes, it expands.
(4) The same is already explained in (1).
(5) It is extremely biologically relevant because it is considered as the universal solvent.
