Buying a kid a games console, imo, is very sad. Kids should be doing stuff not faffing about on consoles. Fat kids die young! My daughter will not be having one EVER whilst she lives at home!
Aaaah the typical twaddle!
If parents control usage games consoles are fine and can be beneficial to learning – reading/problem solving etc.
Our daughter has used them since 5 ( now 8 ) but she also cycles, walks, roller blades, rides horses, reads, etc., etc.
To answer the OP – I’d get a Wii – much easier to control usage than a DS, great range of kids games and you can interact with your kids in the games too (which you will!)