Here is a link on ratings for games and what they mean(from 'Game Stop'):
http://www.gamestop.com/Ratings
Game Stop, the store and online... is a place we get a lot of games from... they also have 2nd hand ones that are CHEAP. Lots of "kid" games too. If anything, they have always been helpful when we ask questions. There are lots of "educational" type games too, that are fun.
Here is an example of their "kid" games and even 2nd hand ones:
http://www.gamestop.com/browse/search.aspx?N=0&Ntk=Ti...
Your daughter is 6 years old, and your son is 10 years old... this is a wide spread in age, to me. So get games that would be suitable for their ages. Not just clumping them together.
We have an XBox.... my hubby got it for himself, and now the kids play on it too, their own "kid" games. My hubby likes it. But his friend likes Playstation.
BUT, each person is different.
Here is the link from Game Stop on Nintendo DS:
http://www.gamestop.com/browse/search.aspx?N=0&Ntk=Ti...
I guess the thing is, if you want a "hand-held" type game thing, or something you can play at home on the tv.
Or, there is the "Wii" gaming system too.... and adults can also get accessories for themselves too, like the "Wii Fit" things which is real popular. But yes, these things are expensive.
Or, maybe try Ebay... they might have some good deals... but you wouldn't have the same return/exchange policies as an actual "store."
Good luck,
Susan