go to manufactorer's website and ask them - or pop into Argos and see one - the advert does not state size of MP3 storage - either hard drive or t'other
It's a CD player, but it can also play CDs that have mp3s on them (as well as standard audio CDs that will play in all other CD players).
As for getting a present for your son; how old is he? If he's only young then this may be an ideal gift; either this or a cheap-ish mp3 player, something like this: