DSiXL Vs 3DS

My daughter replaced her old regular DS with the 3DS. You can turn the 3D part off with a slider (she likes it about 1/4 of the way on). DS games will fit in the 3DS but not vice versa. She likes the "joystick" that is on the 3DS and not on the DSi et al. I found this comparison on About.com:
1) The Nintendo 3DS has a gyroscope and an accelerometer, and the DSi doesn't. In certain 3DS games, you can control the on-screen action by tilting the 3DS unit up and down, or by turning it side-to-side. This is all thanks to the magic of a built-in gyroscope and accelerometer. Not every game utilizes these features, however, and many that do also lets the player utilize a traditional control scheme.
2) The Nintendo 3DS features backwards compatibility for Nintendo DS games. If you buy a Nintendo 3DS, you won't have to leave your DS library behind. The 3DS plays DS games (and, by extension, DSi games) via the game card slot in the back of the system.
3) Both the DSi and the 3DS can download DSiWare. DSiWare" is Nintendo's term for original, downloadable games developed for the DSi. Both the Nintendo 3DS and DSi can download DSiWare as long as you have access to a Wi-Fi connection.
4) The Nintendo 3DS can download and play Game Boy Color Games, and the DSi can't. Nintendo's "eShop," accessible through the 3DS via a Wi-Fi connection, is stocked with retro Game Boy and Game Boy Color titles. You can download and play these blasts from the past for a certain price.
5) You can make Miis with the Nintendo 3DS, but not the DSi
The pudgy avatars that defined the social Wii experience are now on hand to help you personalize your 3DS. Only this time, you can crate a Mii from scratch--or you can take a photo of yourself with the 3DS's camera and sit back while your face is instantly rendered Mii-style! You can share your Mii with other 3DS owners, even when you're carrying the system around in Sleep mode (closed). Wii owners can also transfer their Miis to their 3DS, though not vice-versa.
6) The Nintendo 3DS features unique pack-in software. The Nintendo 3DS comes pre-loaded with software that's meant to show off its 3D capabilities and help you enjoy the system's features to their fullest. This software includes the eShop (wherein you can download Game Boy and Game Boy Advance Games), the Mii maker, the Mii Plaza (wherein you can organize and swap your Miis), "Augmented Reality" games like "Face Raiders" and "Archery" that use the 3DS's cameras to bring the background to life and place them in a virtual world, and an internet browser.
7) The Nintendo 3DS can play mp3s from an SD card, and the DSi can't
The 3DS can play mp3 and AAC music files from an SD card. The DSi can play AAC files from an SD card, but doesn't support mp3 files.

I was going to get the DSiXL for our 10 year old but went with the 3DS instead. It does say right in the packaging that kids under 7 should not use it though. We bought it knowing that it was backwards compatible with other ds games and the 3D can be turned down and off. The instructions caution against using the 3D feature for more than 15 minutes at a time. There aren't a ton of 3d games out now but more are on the way. Also the 3DS and the DSiXL are the same price now. If you got her the 3DS you wouldn't be able to allow her to use all the features until she is older but you would have the latest technology. If you don't think that would go over well, then go with the other. There are and will be a ton of games available for a while.

Your daughter is too young for the 3DS. The age recommendation is 8+. It seems that if you are younger than 7y it messes with your eyes.

My son has the XLi and LOVES it.

The 3ds gives me a headache.
I don't think a 6 yr old needs a DS. But if you are goign to get her one , go with the DS lite, DSi or the DSi XL. only difference between the DSi and DSi XL is the size and the cost. the DS lite is the older machine, plays gameboy games as well as DS games. This is the system I prefer because there is more out there for it and you can get more used games for it.

My kid loves to watch other kids play but can't w/his friend who has 3DS b/c you literally can't see anything unless you are sitting right in front of the screen, which obviously would get in the player's way.

Get the XL...we got it b/c of the bigger screen and I love playing on it myself!

don't get the 3ds for a kid under 8. period. their eyes aren't ready for that. dsixl is still amazing.

Ohhhhh , great question! That's what we are getting the kids too - I'm going with the XL (I think), but look forward to reading these responses

Thanks!