It is possible, but via another way.

Put msd to pc and search for globalsettings.ini file, open it and edit this row : LockStartMenu = 0

instead of 0 put 1 there and save.

This locks the start menu, so no one could go to menu and do anything there. No START no DELETE

And on filetrip is one small homebrew aplication (which name I dont remember), but it allows to LOCK the whole DS Flashcard with PASSWORD...

EDIT: http://filetrip.net/f6893-DSecure-81309.html
btw. it doesnt work on AK2i, so it is useless, sorry

 

I am really shocked that there isn't any way. I would have thought that someone would have come up with a way to do it ages ago.

 

it locks the start menu, but can't someone just play a game and overwrite your save anyway?

 

Don't let them play with it?

 

Thanks for the suggestions guys.
The reason I'm looking for a password protect solution is help protect the save games on my 9 year old son's DS.
My 3 year old keeps getting hold of the 9yo's DS (he can't reach the top of the fridge either!) and playing/deleting/overwriting his saved games.
He just burst into tears after realising he had lost the last 106 solutions to Picross 3D!
He'll learn, but it'd be nice if it could be avoided in the first place (there's a 6yo and a 1yo in the house as well!)