Hi ipod are good I wont say anything against them
but you must have itunes installed and my opinion it is a bit of a pain to use (my eldest Daughter has one she spends ages getting her music sorted) where as myself and my youngest Daughter have mp3 players it is as simple as copy and paste or drag and drop to get your music across!
and of course as you have already mentioned the price
the ipod shuffle is £49 approx the ipod Nano being considerably more about a £140 it would really depend on how old they are and what you wanted to spend
but in saying all this the ipod is the in thing for the youngsters and they have got to have the latest eh!
good luck on what ever you decide one things for sure your Bank Balance will drop whatever you decide to get them :-)