I do think you should look at one of the Phantom Hybrids. Either the Phantom from 2007 or the Phantom Race 320 from the 2008 line.
It has a dagger which makes it usable and fun in light winds, and a lot more fun as a learning platform for the family. It is wide enough to be sufficiently stable, and narrow enough to work well with the dagger down.
Short and wide boards are like barges in subplaning conditions, they are made ONLY for planing. A boardlength of about 300 cm starts to give you some glide (and thus fun) in light winds. At the same time teh Phantom will be a perfectly good planing blaster.
When you develop on this board and get a lot better I think it makes sense to complement the Phantom with a board in the 110 liter range, i.e. a true shortboard. You can just skip the boards in between.