Retail games? If the DS can't read the save on many of your retail games, then you might have build up on the contacts. Is it possible something was spilled on them?
Try taking a Q-tip with a very little bit of rubbing alcohol and carefully cleaning the contacts (the gold pins in slot-1). Try cleaning the contacts on the games too.
Another possibility, if your daughter uses the same games over and over again, is that the game cartridges have worn, and are loose in the slot. You could try folding a small piece of paper, and wedging it behind the game so it makes better contact and doesn't move around.
If neither of those work, you might have a defective DS on your hands.
If I've misunderstood, and you're talking about roms on a flashcart, then you need to tell us what flashcart, firmware, etc.