I think that for long journeys and things, they are a help, they just need to be used in moderation. As long as your children interact at other times, i don't see the harm in having them. My son becames exactly the same when playing with lego - he goes into a world of his own and grunts in response. However when he and his brother are playing on their PS2 - they are jumping about, laughing and interacting together. I think that there are good points and bad points - everything in moderation I think.