I think they are good in moderation, But children should still be encourage to play with actual toys and other things.
Are mobile phones good for children?
I should ask myself this question!
These days the mobile phone is a sign of status and this is a very tricky thing - those parents who don't have money for the latest version of a mobile phone puts their kids in "trouble", everybody has the phone and their kid doesn't.
It's a huge problem IMO besides the stealing of a expensive device and seeing your boy or girl coming home crying...