Wots wrong with my DS?Edge?

Hey everyone , complete newb here so please be gentle,
problem : I bought my two neices an edge card each for christmas , both cards work fine in one of their ds lite's but neither card will work in the newer ds , my brother bought other child a new ds for xmas.
when cartridge is inserted in newer machine nothing happens , i think the onscreen message says no card inserted. Is there a setting i can change so it see's the card?
any help appreciated as both kids fighting over the one with all the games :mad:!ta

Hey just to answer my own problem , might help someone.
Apparently some r4 cards dont quite fit properly so therefore don't connect properly when inserted , brother fixed my neice;s by carefully 'packing out' with a little piece of card, thanks.