Hi there. You stated "5 big consoles" but there are only really 3 at the moment. maybe it was just a mistake!
Anyway. For a 5 year old I think your best bet would be the Game Cube.
It is geared towards the younger generation and has lots of games that will appeal to a younger person.
It is much cheaper than the other consoles, but the software isnt. But again thats roughly the same for the other consoles too!
Unfortuntely, the GC cant play N64 games since the N64 is a cartridge based machine and the GC is a Disk based system.
The PS2 is a good machine with a huge library of games and as you said a huge back catalog of PS1 games too.
As for learning games, not that many, and for those I think the PC is a better format.
There are also the Nintendo Game Boy Advance which is popular ammong children, and is very cheap.
And also later this year a new handheld called Nintendo "DS" that might also be interesting for young children.
These 2 handhelds are also backwards compatible, so you could buy older cheaper GBA games and still play them on the DS for example.
Do a search on the DS to get an idea of what it can do.
Just remember, a games console isnt just for Xmas, its for life!
Hope this helps!