FYI.
I got my 7 year old daughter a DSTT and she is using a SanDisk 8GB MicroSDHC with no problems (using the DSTT OS v1.12/). I put 213 game/rom .nds files in a folder I named "roms" on the root of the memory card. Every game she has played works great! Also one thing to remember is to leave some free space for the .sav files. Looks like each one takes 512KB. I haven't messed around with MoonShell yet. Her card is full and she doesn't listen to music much and she can watch movies on my BlackBerry or on the TV at home.
If any one has concerns over getting a DSTT...I have experienced none. This thing is awesome!
Another good place to get games/roms is the torrent sites. So far I have a total of 603 games (99% of them English). [URL deleted] is good too, but very slow.