I would get a 2DS for a child (I work in a game shop and have handled them all), namely for these reasons:
- No hinges, so therefore no hinge breakages which is a common complaint with other types
- Same features as the 3DS such as augmented reality features, internet browser etc. It's just without the 3D (which isn't suitable for under 7s anyway)
- Rather cheap price, only £109.99 new.
- Nice chunky buttons and surprisingly compact for small hands.
- Playable with 3DS games (I would say this should be the biggest factor in your decision). 3DS games have superior graphics and whilst not announced yet, with the 2DS I can see regular DS games to eventually be weaned off the market. So IMO, your DS/DS lites will soon be outdated, and I would say the 2DS is worth the extra money for longevity value.
- Bigger, harder to lose stylus.
If you go into your local GAME, ask the staff and they should have one out and ready to let you try