I went to the local store last and purchased a red ds lite there for my ds who will turn 7 in May. He has been asking for one for over a year and says he's the only one in his class without one - doubt this. We too will limit his time on it. In our house, it replaces tv time.
My ds 9 got a ds lite for his 9th birthday. He was not into video games but we bought him one because he is very shy and we felt it would help him socialize with kids his own age better. He is very quiet and found it hard to strike up a conversation. He would say to us - all they talk about is video games. he doesn't play that much with his - but it really did help him socially. He knows what the other kids are talking about now and is able to join in the conversation.
